Articles de revistahttp://hdl.handle.net/2117/3952021-08-02T07:14:46Z2021-08-02T07:14:46ZIonic polaron in a Bose-Einstein condensateAstrakharchik, GrigoriSchmidt, Richardhttp://hdl.handle.net/2117/3492202021-07-18T21:01:21Z2021-07-13T15:14:49ZIonic polaron in a Bose-Einstein condensate
Astrakharchik, Grigori; Schmidt, Richard
The presence of strong interactions in a many-body quantum system can lead to a variety of exotic effects. Here we show that even in a comparatively simple setup consisting of a charged impurity in a weakly interacting bosonic medium the competition of length scales gives rise to a highly correlated mesoscopic state. Using quantum Monte Carlo simulations, we unravel its vastly different polaronic properties compared to neutral quantum impurities. Moreover, we identify a transition between the regime amenable to conventional perturbative treatment in the limit of weak atom-ion interactions and a many-body bound state with vanishing quasi-particle residue composed of hundreds of atoms. In order to analyze the structure of the corresponding states, we examine the atom-ion and atom-atom correlation functions which both show nontrivial properties. Our findings are directly relevant to experiments using hybrid atom-ion setups that have recently attained the ultracold regime.
2021-07-13T15:14:49ZAstrakharchik, GrigoriSchmidt, RichardThe presence of strong interactions in a many-body quantum system can lead to a variety of exotic effects. Here we show that even in a comparatively simple setup consisting of a charged impurity in a weakly interacting bosonic medium the competition of length scales gives rise to a highly correlated mesoscopic state. Using quantum Monte Carlo simulations, we unravel its vastly different polaronic properties compared to neutral quantum impurities. Moreover, we identify a transition between the regime amenable to conventional perturbative treatment in the limit of weak atom-ion interactions and a many-body bound state with vanishing quasi-particle residue composed of hundreds of atoms. In order to analyze the structure of the corresponding states, we examine the atom-ion and atom-atom correlation functions which both show nontrivial properties. Our findings are directly relevant to experiments using hybrid atom-ion setups that have recently attained the ultracold regime.Structural superfluid-Mott-insulator transition for a Bose gas in multirodsRodríguez López, Omar AbelBoronat Medico, Jordihttp://hdl.handle.net/2117/3455332021-05-16T21:49:22Z2021-05-13T07:31:09ZStructural superfluid-Mott-insulator transition for a Bose gas in multirods
Rodríguez López, Omar Abel; Boronat Medico, Jordi
We report on a structural superfluid–Mott-insulator (SF-MI) quantum phase transition for an interacting one-dimensional Bose gas within permeable multirod lattices, where the rod lengths are varied from zero to the lattice period length. We use the ab initio diffusion Monte Carlo method to calculate the static structure factor, the insulation gap, and the Luttinger parameter, which we use to determine if the gas is a superfluid or a Mott insulator. For the Bose gas within a square Kronig-Penney (KP) potential, where barrier and well widths are equal, the SF-MI coexistence curve shows the same qualitative and quantitative behavior as that of a typical optical lattice with equal periodicity but slightly larger height. When we vary the width of the barriers from zero to the length of the potential period, keeping the height of the KP barriers, we observe a way to induce the SF-MI phase transition. Our results are of significant interest, given the recent progress on the realization of optical lattices with a subwavelength structure that would facilitate their experimental observation.
2021-05-13T07:31:09ZRodríguez López, Omar AbelBoronat Medico, JordiWe report on a structural superfluid–Mott-insulator (SF-MI) quantum phase transition for an interacting one-dimensional Bose gas within permeable multirod lattices, where the rod lengths are varied from zero to the lattice period length. We use the ab initio diffusion Monte Carlo method to calculate the static structure factor, the insulation gap, and the Luttinger parameter, which we use to determine if the gas is a superfluid or a Mott insulator. For the Bose gas within a square Kronig-Penney (KP) potential, where barrier and well widths are equal, the SF-MI coexistence curve shows the same qualitative and quantitative behavior as that of a typical optical lattice with equal periodicity but slightly larger height. When we vary the width of the barriers from zero to the length of the potential period, keeping the height of the KP barriers, we observe a way to induce the SF-MI phase transition. Our results are of significant interest, given the recent progress on the realization of optical lattices with a subwavelength structure that would facilitate their experimental observation.Bridging NiCo layered double hydroxides and Ni3S2 for bifunctional electrocatalysts: the role of vertical grapheneXiao, ZhangFan, JiajunLu, XunyuHan, ZhaojunCazorla Silva, ClaudioHu, LongWu, TomChu, Deweihttp://hdl.handle.net/2117/3454092021-06-06T09:20:18Z2021-05-11T08:44:20ZBridging NiCo layered double hydroxides and Ni3S2 for bifunctional electrocatalysts: the role of vertical graphene
Xiao, Zhang; Fan, Jiajun; Lu, Xunyu; Han, Zhaojun; Cazorla Silva, Claudio; Hu, Long; Wu, Tom; Chu, Dewei
In this work, we report a bifunctional electrocatalyst with nickel sulphide (Ni3S2) as the template, vertical graphene (VG) as the bridging material, and nickel–cobalt layered double hydroxides (NiCo LDHs) nanosheets as the active catalyst. The hybrid Ni3S2/VG@NiCo LDHs catalyst exhibits excellent activity in alkaline solution for both OER (overpotential ~ 320 mV at a current density of 100 mA cm-2) and HER (overpotential ~ 120 mV at a current density of 10 mA cm-2). In addition, the hybrid catalyst possesses superior stability with 99% retention of voltage upon a continued current density of 20 mV cm-2 for over 24 h. It is found that the transitions of Ni2+/Ni3+ and Co2+/Co3+ ions enable excellent HER and OER performances, and VG bridging between NiCo LDHs and Ni3S2, enable fast charge-transfer and a high density of active sites, resulting in the improved electrical conductivity, intrinsic activity, and electrochemical stability. This work provides a guideline to design the architecture of bifunctional catalysts for highly efficient water splitting applications.
2021-05-11T08:44:20ZXiao, ZhangFan, JiajunLu, XunyuHan, ZhaojunCazorla Silva, ClaudioHu, LongWu, TomChu, DeweiIn this work, we report a bifunctional electrocatalyst with nickel sulphide (Ni3S2) as the template, vertical graphene (VG) as the bridging material, and nickel–cobalt layered double hydroxides (NiCo LDHs) nanosheets as the active catalyst. The hybrid Ni3S2/VG@NiCo LDHs catalyst exhibits excellent activity in alkaline solution for both OER (overpotential ~ 320 mV at a current density of 100 mA cm-2) and HER (overpotential ~ 120 mV at a current density of 10 mA cm-2). In addition, the hybrid catalyst possesses superior stability with 99% retention of voltage upon a continued current density of 20 mV cm-2 for over 24 h. It is found that the transitions of Ni2+/Ni3+ and Co2+/Co3+ ions enable excellent HER and OER performances, and VG bridging between NiCo LDHs and Ni3S2, enable fast charge-transfer and a high density of active sites, resulting in the improved electrical conductivity, intrinsic activity, and electrochemical stability. This work provides a guideline to design the architecture of bifunctional catalysts for highly efficient water splitting applications.Superfluid vortex dynamics on a torus and other toroidal surfaces of revolutionGuenther, Nils EricMassignan, Pietro AlbertoFetter, Alexander L.http://hdl.handle.net/2117/3453622021-05-16T21:46:56Z2021-05-10T11:03:57ZSuperfluid vortex dynamics on a torus and other toroidal surfaces of revolution
Guenther, Nils Eric; Massignan, Pietro Alberto; Fetter, Alexander L.
The superfluid flow velocity is proportional to the gradient of the phase of the superfluid order
parameter, leading to the quantization of circulation around a vortex core. In this work, we study
the dynamics of a superfluid film on the surface of a torus. Such a compact surface allows only
configurations of vortices with zero net vorticity. We derive analytic expressions for the flow field,
the total energy, and the time-dependent dynamics of the vortex cores. The local curvature of the
torus and the presence of non-contractable loops on this multiply connected surface alter both the
superfluid flow and the vortex dynamics. Finally we consider more general surfaces of revolution,
called toroids
2021-05-10T11:03:57ZGuenther, Nils EricMassignan, Pietro AlbertoFetter, Alexander L.The superfluid flow velocity is proportional to the gradient of the phase of the superfluid order
parameter, leading to the quantization of circulation around a vortex core. In this work, we study
the dynamics of a superfluid film on the surface of a torus. Such a compact surface allows only
configurations of vortices with zero net vorticity. We derive analytic expressions for the flow field,
the total energy, and the time-dependent dynamics of the vortex cores. The local curvature of the
torus and the presence of non-contractable loops on this multiply connected surface alter both the
superfluid flow and the vortex dynamics. Finally we consider more general surfaces of revolution,
called toroidsUniversal dimerized quantum droplets in a one-dimensional latticeMorera Navarro, IvánAstrakharchik, GrigoriPolls Martí, ArturJulia Diaz, Brunohttp://hdl.handle.net/2117/3452662021-05-09T18:02:34Z2021-05-06T15:38:48ZUniversal dimerized quantum droplets in a one-dimensional lattice
Morera Navarro, Iván; Astrakharchik, Grigori; Polls Martí, Artur; Julia Diaz, Bruno
The ground-state properties of two-component bosonic mixtures in a one-dimensional optical lattice are studied both from few- and many-body perspectives. We rely directly on a microscopic Hamiltonian with attractive intercomponent and repulsive intracomponent interactions to demonstrate the formation of a quantum liquid. We reveal that its formation and stability can be interpreted in terms of finite-range interactions between dimers. We derive an effective model of composite bosons (dimers) which correctly captures both the few- and many-body properties and validate it against exact results obtained by the density matrix renormalization group method for the full Hamiltonian. The threshold for the formation of the liquid coincides with the appearance of a bound state in the dimer-dimer problem and possesses a universality in terms of the two-body parameters of the dimer-dimer interaction, namely, scattering length and effective range. For sufficiently strong effective dimer-dimer repulsion we observe fermionization of the dimers which form an effective Tonks-Girardeau state and identify conditions for the formation of a solitonic solution. Our predictions are relevant to experiments with dipolar atoms and two-component mixtures.
2021-05-06T15:38:48ZMorera Navarro, IvánAstrakharchik, GrigoriPolls Martí, ArturJulia Diaz, BrunoThe ground-state properties of two-component bosonic mixtures in a one-dimensional optical lattice are studied both from few- and many-body perspectives. We rely directly on a microscopic Hamiltonian with attractive intercomponent and repulsive intracomponent interactions to demonstrate the formation of a quantum liquid. We reveal that its formation and stability can be interpreted in terms of finite-range interactions between dimers. We derive an effective model of composite bosons (dimers) which correctly captures both the few- and many-body properties and validate it against exact results obtained by the density matrix renormalization group method for the full Hamiltonian. The threshold for the formation of the liquid coincides with the appearance of a bound state in the dimer-dimer problem and possesses a universality in terms of the two-body parameters of the dimer-dimer interaction, namely, scattering length and effective range. For sufficiently strong effective dimer-dimer repulsion we observe fermionization of the dimers which form an effective Tonks-Girardeau state and identify conditions for the formation of a solitonic solution. Our predictions are relevant to experiments with dipolar atoms and two-component mixtures.Enhancement of phase stability and optoelectronic performance of BiFeO3 thin films via cation co-substitutionMachado, PamelaCaño, IvanMenendez Muniz, CesarCazorla Silva, ClaudioTan, HuanFina, IgnasiCampoy Quiles, MarioanoEscudero, CarlosTallarida, MassimoColl, Marionahttp://hdl.handle.net/2117/3445592021-06-06T08:14:44Z2021-04-27T11:04:46ZEnhancement of phase stability and optoelectronic performance of BiFeO3 thin films via cation co-substitution
Machado, Pamela; Caño, Ivan; Menendez Muniz, Cesar; Cazorla Silva, Claudio; Tan, Huan; Fina, Ignasi; Campoy Quiles, Marioano; Escudero, Carlos; Tallarida, Massimo; Coll, Mariona
Compositional engineering of BiFeO3 can significantly boost its photovoltaic performance. Therefore, controlling site substitution and understanding how it affects the optical and electronic properties while achieving robust and stable phases is essential to continue progressing in this field. Here the influence of cation co-substitution in BiFeO3 on phase purity, optical and electronic properties is investigated by means of X-ray diffraction, spectroscopic ellipsometry and X-ray absorption spectroscopy, respectively. Piezoelectric force microscopy and ferroelectric characterization at room temperature has been carried out in co-doped BiFeO3 films. First-principles calculations are also performed and compared to the experimental observations. It is shown that the incorporation of La3+ in Bi(Fe,Co)O3 films improves phase purity and stability while preserving the reduced band gap achieved in metastable Bi(Fe,Co)O3. Moreover, it is suggested that the changes in the optoelectronic properties are mainly dictated by the hybridisation between unoccupied Co 3d and O 2p states along with the presence of Co3+/Co2+ species. This thorough study on (Bi,La)(Fe,Co)O3 thin films coupled with the use of a cost-effective and facile solution deposition synthesis increases the motivation to continue exploiting the potential of these perovskite materials.
2021-04-27T11:04:46ZMachado, PamelaCaño, IvanMenendez Muniz, CesarCazorla Silva, ClaudioTan, HuanFina, IgnasiCampoy Quiles, MarioanoEscudero, CarlosTallarida, MassimoColl, MarionaCompositional engineering of BiFeO3 can significantly boost its photovoltaic performance. Therefore, controlling site substitution and understanding how it affects the optical and electronic properties while achieving robust and stable phases is essential to continue progressing in this field. Here the influence of cation co-substitution in BiFeO3 on phase purity, optical and electronic properties is investigated by means of X-ray diffraction, spectroscopic ellipsometry and X-ray absorption spectroscopy, respectively. Piezoelectric force microscopy and ferroelectric characterization at room temperature has been carried out in co-doped BiFeO3 films. First-principles calculations are also performed and compared to the experimental observations. It is shown that the incorporation of La3+ in Bi(Fe,Co)O3 films improves phase purity and stability while preserving the reduced band gap achieved in metastable Bi(Fe,Co)O3. Moreover, it is suggested that the changes in the optoelectronic properties are mainly dictated by the hybridisation between unoccupied Co 3d and O 2p states along with the presence of Co3+/Co2+ species. This thorough study on (Bi,La)(Fe,Co)O3 thin films coupled with the use of a cost-effective and facile solution deposition synthesis increases the motivation to continue exploiting the potential of these perovskite materials.Nature of alkali ion conduction and reversible Na-ion storage in hybrid formate framework materialsPolek, AnnaCazorla Silva, ClaudioKundu, Dipanhttp://hdl.handle.net/2117/3445382021-06-06T05:07:24Z2021-04-27T08:41:50ZNature of alkali ion conduction and reversible Na-ion storage in hybrid formate framework materials
Polek, Anna; Cazorla Silva, Claudio; Kundu, Dipan
The cost advantage of Na-ion batteries has spurred intensive research effort in the last ten years to develop reversible Na+ storage materials. While classic host materials – analogous to the Liion system – are potentially straightforward targets, sluggish Na+ diffusion in many inorganic structures limit options. In this regard, open framework inorganic-organic hybrids like metalorganic framework materials are considered as viable alternatives. Herein we introduce heterometallic formate frameworks as potential candidates for reversible Na+ storage. In a first, we present a microwave solvothermal strategy for rapid synthesis of phase pure microcrystalline Na2Co(HCO2)4 and AB(HCO2)3 (A: Li/Na; B: Co/Mn). By combining indepth impedance analysis with ab-initio molecular dynamics simulation, we reveal that the Li+ /Na+ conduction – which follows a ‘pinball’ mechanism – in these materials is extrinsic defect dominated. Calculation suggests that a librational motion of the formate anions facilitates the diffusion of Na+ compared to Li+ , explaining the origin of anomalously higher ionic conductivity for the Na analogue compared to the Li one. Preliminary electrochemical investigation reveals reversible Na+ storage in Na2Co(HCO2)4 and NaMn(HCO2)3 at an average voltage of 2.5-3 V.
2021-04-27T08:41:50ZPolek, AnnaCazorla Silva, ClaudioKundu, DipanThe cost advantage of Na-ion batteries has spurred intensive research effort in the last ten years to develop reversible Na+ storage materials. While classic host materials – analogous to the Liion system – are potentially straightforward targets, sluggish Na+ diffusion in many inorganic structures limit options. In this regard, open framework inorganic-organic hybrids like metalorganic framework materials are considered as viable alternatives. Herein we introduce heterometallic formate frameworks as potential candidates for reversible Na+ storage. In a first, we present a microwave solvothermal strategy for rapid synthesis of phase pure microcrystalline Na2Co(HCO2)4 and AB(HCO2)3 (A: Li/Na; B: Co/Mn). By combining indepth impedance analysis with ab-initio molecular dynamics simulation, we reveal that the Li+ /Na+ conduction – which follows a ‘pinball’ mechanism – in these materials is extrinsic defect dominated. Calculation suggests that a librational motion of the formate anions facilitates the diffusion of Na+ compared to Li+ , explaining the origin of anomalously higher ionic conductivity for the Na analogue compared to the Li one. Preliminary electrochemical investigation reveals reversible Na+ storage in Na2Co(HCO2)4 and NaMn(HCO2)3 at an average voltage of 2.5-3 V.Giant thermal enhancement of the electric polarization in ferrimagnetic BiFe_{1-x}Co_{x}O_{3} solid solutions near room temperatureMenendez Muniz, CesarCazorla Silva, Claudiohttp://hdl.handle.net/2117/3440602021-06-06T04:17:19Z2021-04-21T08:34:36ZGiant thermal enhancement of the electric polarization in ferrimagnetic BiFe_{1-x}Co_{x}O_{3} solid solutions near room temperature
Menendez Muniz, Cesar; Cazorla Silva, Claudio
Thermal excitations typically reduce the electric polarization in ferroelectric materials. Here, we show by means of first-principles calculations that multiferroic BiFe 1 - x Co x O 3 solid solutions with 0.25 = x = 0.50 (BFCO) represent a noteworthy exception to this behavior. In particular, we find that, at room temperature and for moderate pressures of 0.1–1.0 GPa, depending on the composition, the electric polarization of bulk BFCO increases by ~ 150 % . The origin of such an exceptional behavior is a phase transformation involving a low- T rhombohedral ( R ) phase and a high- T supertetragonal ( T ) phase. Both R and T phases are ferrimagnetic near room temperature with an approximate net magnetization of 0.13 µ B per formula unit. Contrary to what occurs in either bulk BiFeO 3 or BiCoO 3 , the T phase is stabilized over the R by increasing temperature due to its higher vibrational entropy. This extraordinary T -induced R ¿ T phase transition is originated by polar phonon modes that involve concerted displacements of transition-metal and oxygen ions.
2021-04-21T08:34:36ZMenendez Muniz, CesarCazorla Silva, ClaudioThermal excitations typically reduce the electric polarization in ferroelectric materials. Here, we show by means of first-principles calculations that multiferroic BiFe 1 - x Co x O 3 solid solutions with 0.25 = x = 0.50 (BFCO) represent a noteworthy exception to this behavior. In particular, we find that, at room temperature and for moderate pressures of 0.1–1.0 GPa, depending on the composition, the electric polarization of bulk BFCO increases by ~ 150 % . The origin of such an exceptional behavior is a phase transformation involving a low- T rhombohedral ( R ) phase and a high- T supertetragonal ( T ) phase. Both R and T phases are ferrimagnetic near room temperature with an approximate net magnetization of 0.13 µ B per formula unit. Contrary to what occurs in either bulk BiFeO 3 or BiCoO 3 , the T phase is stabilized over the R by increasing temperature due to its higher vibrational entropy. This extraordinary T -induced R ¿ T phase transition is originated by polar phonon modes that involve concerted displacements of transition-metal and oxygen ions.Amplitude death and restoration in networks of oscillators with random-walk diffusionClusella Coberó, PauPastor Satorras, Romualdohttp://hdl.handle.net/2117/3438862021-04-25T19:02:41Z2021-04-19T12:06:10ZAmplitude death and restoration in networks of oscillators with random-walk diffusion
Clusella Coberó, Pau; Pastor Satorras, Romualdo
Systems composed of reactive particles diffusing in a network display emergent dynamics. While Fick’s diffusion can lead to Turing patterns, other diffusion schemes might display more complex phenomena. Here we study the death and restoration of collective oscillations in networks of oscillators coupled by random-walk diffusion, which modifies both the original unstable fixed point and the stable limit-cycle, making them topology-dependent. By means of numerical simulations we show that, in some cases, the diffusion-induced heterogeneity stabilizes the initially unstable fixed point via a Hopf bifurcation. Further increasing the coupling strength can moreover restore the oscillations. A numerical stability analysis indicates that this phenomenology corresponds to a case of amplitude death, where the inhomogeneous stabilized solution arises from the interplay of random walk diffusion and heterogeneous topology. Our results are relevant in the fields of epidemic spreading or ecological dispersion, where random walk diffusion is more prevalent.
2021-04-19T12:06:10ZClusella Coberó, PauPastor Satorras, RomualdoSystems composed of reactive particles diffusing in a network display emergent dynamics. While Fick’s diffusion can lead to Turing patterns, other diffusion schemes might display more complex phenomena. Here we study the death and restoration of collective oscillations in networks of oscillators coupled by random-walk diffusion, which modifies both the original unstable fixed point and the stable limit-cycle, making them topology-dependent. By means of numerical simulations we show that, in some cases, the diffusion-induced heterogeneity stabilizes the initially unstable fixed point via a Hopf bifurcation. Further increasing the coupling strength can moreover restore the oscillations. A numerical stability analysis indicates that this phenomenology corresponds to a case of amplitude death, where the inhomogeneous stabilized solution arises from the interplay of random walk diffusion and heterogeneous topology. Our results are relevant in the fields of epidemic spreading or ecological dispersion, where random walk diffusion is more prevalent.Effect of the water model in simulations of protein–protein recognition and associationEmperador Badimon, AgustínCrehuet Simón, RamonGuàrdia Manuel, Elvirahttp://hdl.handle.net/2117/3425672021-03-29T01:01:57Z2021-03-26T10:46:01ZEffect of the water model in simulations of protein–protein recognition and association
Emperador Badimon, Agustín; Crehuet Simón, Ramon; Guàrdia Manuel, Elvira
We study self-association of ubiquitin and the disordered protein ACTR using the most commonly used water models. We find that dissociation events are found only with TIP4P-EW and TIP4P/2005, while the widely used TIP3P water model produces straightforward aggregation of the molecules due to the absence of dissociation events. We also find that TIP4P/2005 is the only water model that reproduces the fast association/dissociation dynamics of ubiquitin and best identifies its binding surface. Our results show the critical role of the water model in the description of protein–protein interactions and binding.
2021-03-26T10:46:01ZEmperador Badimon, AgustínCrehuet Simón, RamonGuàrdia Manuel, ElviraWe study self-association of ubiquitin and the disordered protein ACTR using the most commonly used water models. We find that dissociation events are found only with TIP4P-EW and TIP4P/2005, while the widely used TIP3P water model produces straightforward aggregation of the molecules due to the absence of dissociation events. We also find that TIP4P/2005 is the only water model that reproduces the fast association/dissociation dynamics of ubiquitin and best identifies its binding surface. Our results show the critical role of the water model in the description of protein–protein interactions and binding.