Monolayer FeSe films grown on SrTiO_3(STO)substrate show superconducting gap-opening temperatures(T_c) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based...Monolayer FeSe films grown on SrTiO_3(STO)substrate show superconducting gap-opening temperatures(T_c) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductors. Angle-resolved photoemission spectroscopy observed ‘‘replica bands' ' suggesting the importance of the interaction between FeSe electrons and STO phonons. These facts rejuvenated the quest for T_c enhancement mechanisms in iron-based, especially ironchalcogenide, superconductors. Here, we perform the first numerically-exact sign-problem-free quantum Monte Carlo simulations to iron-based superconductors. We(1) study the electronic pairing mechanism intrinsic to heavily electron doped FeSe films, and(2) examine the effects of electron–phonon interaction between FeSe and STO as well as nematic fluctuations on T_c. Armed with these results, we return to the question ‘‘what makes the Tcof monolayer FeSe on SrTiO_3 so high?'' in the conclusion and discussions.展开更多
The rattling mode,an anharmonic vibrational phonon,is widely recognized as a critical factor in the emergence of superconductivity in caged materials.Here,we present a counterexample in a filled-skutterudite supercond...The rattling mode,an anharmonic vibrational phonon,is widely recognized as a critical factor in the emergence of superconductivity in caged materials.Here,we present a counterexample in a filled-skutterudite superconductor Ba_(x)Ir_(4)Sb_(12)(x=0.8,0.9,1.0),synthesized via a high-pressure route.Transport measurements down to liquid 3He temperatures reveal a transition temperature(T_(c))of 1.2 K and an upper critical field(H_(c2))of 1.3 T.Unlike other superconductors with caged structures,the Ba_(x)Ir_(4)Sb_(12)(X=P,As,Sb)family exhibits a monotonic decreasing T_(c) with the enhancement of the rattling mode,as indicated by fitting the Bloch–Grüneisen formula.Theoretical analysis suggests that electron doping from Ba transforms the direct bandgap IrSb3 into a metal,with the Fermi surface dominated by the hybridization of Ir 5d and Sb 5p orbitals.Our findings of decoupled rattling modes and superconductivity distinguish the Ba_(x)Ir_(4)Sb_(12) family from other caged superconductors,warranting further exploration into the underlying mechanism.展开更多
Electron density differences resulting from atom displacement patterns aligned with phonon modes in MgB2 have been calculated using density functional theory (DFT). The extent of phonon anomalies, identified as indica...Electron density differences resulting from atom displacement patterns aligned with phonon modes in MgB2 have been calculated using density functional theory (DFT). The extent of phonon anomalies, identified as indicators of the superconducting transition temperature, Tc, under a range of conditions in AlB2-type structures, reduce as boron atoms are displaced from their equilibrium positions along E2g mode directions. The Fermi energy for displacements along the directions of the E2g phonon mode accounts for changes in the covalent B-B bond electronic charge density. We applied differential atom displacements to show that the shifted σ band structure associated with the light effective mass became tangential to the Fermi level and that the Fermi surface undergoes a topological transition at a critical relative displacement of ~0.6% of the boron atoms from equilibrium. The difference in Fermi energies at this critical displacement and at the equilibrium position correspond to the superconducting energy gap. The net volume between tubular σ surfaces in reciprocal space correlated with the depth of the phonon anomaly and, by inference, it is a key to an understanding of superconductivity. This ab initioapproach offers a phenomenological understanding of the factors that determine Tc based on knowledge of the crystal structure.展开更多
This paper is concerned with the minimization problem related to the superconductivity with thermal noise. We study the asymptotic behavior of the minimizes of this problem as the parameters tending to zero and prove ...This paper is concerned with the minimization problem related to the superconductivity with thermal noise. We study the asymptotic behavior of the minimizes of this problem as the parameters tending to zero and prove the vortices-pinning mechanism.展开更多
Studying the complexity of the electronic phase diagram is at the heart of understanding strongly correlated system in general,with high Tc superconductors as the most known examples.High temperature superconductivity...Studying the complexity of the electronic phase diagram is at the heart of understanding strongly correlated system in general,with high Tc superconductors as the most known examples.High temperature superconductivity has a wide range of application potentials in power transmission,nuclear magnetic resonance,magnetic levitation transportation,aerospace,information and communication technologies,etc.Understanding its mechanism remains a long-standing challenge,due to its complex material structures and interlays among different phases such as charge density wave,antiferromagnetic and superconducting phases.As a result,this has greatly hindered its further development.展开更多
For the superconductors(Rb_xK_(1-x))_3C_(60)(x=0.1),according to BCS theory and assuming that the virtual phonon acting on electron-pair is corresponding to the intrasolecular vibration in the bnckminnterfullerene C_(...For the superconductors(Rb_xK_(1-x))_3C_(60)(x=0.1),according to BCS theory and assuming that the virtual phonon acting on electron-pair is corresponding to the intrasolecular vibration in the bnckminnterfullerene C_(60),a linear relationship of the superconducting transition temperature T_c with x has been derived,which is in agreement with the experimentals,展开更多
It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces,characterized by a nonintegrable phase factor that an elementary particle of charge q ac...It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces,characterized by a nonintegrable phase factor that an elementary particle of charge q acquires from A to B points:P exp(iq/hc∫A^(B)A_(μ)dxμ),where Aμis the gauge potential and P stands for path ordering.In a many-body system of strongly correlated electrons,if the so-called Mott gap is opened up by interaction,the corresponding Hilbert space will be fundamentally changed.A novel nonintegrable phase factor known as phase-string will appear and replace the conventional Fermi statistics to dictate the low-lying physics.Protected by the Mott gap,which is clearly identified in the high-Tc cuprate with a magnitude>1.5 e V,such a singular phase factor can enforce a fractionalization of the electrons,leading to a dual world of exotic elementary particles with a topological gauge structure.A non-Fermi-liquid“parent”state will emerge,in which the gapless Landau quasiparticle is only partially robust around the so-called Fermi arc regions,while the main dynamics are dominated by two types of gapped spinons.Antiferromagnetism,superconductivity,and a Fermi liquid with full Fermi surface can be regarded as the low-temperature instabilities of this new parent state.Both numerics and experiments provide direct evidence for such an emergent physics of the Mottness,which lies in the core of a high-Tc superconducting mechanism.展开更多
基金the National Supercomputer Center in Guangzhou for computational supportZXL and HY were supported in part by the National Thousand Young-Talents Program and the National Natural Science Foundation of China (11474175)+1 种基金FW was supported by the National Natural Science Foundation of China (11374018)DHL was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Grant DE-AC0205CH11231
文摘Monolayer FeSe films grown on SrTiO_3(STO)substrate show superconducting gap-opening temperatures(T_c) which are almost an order of magnitude higher than those of the bulk FeSe and are highest among all known Fe-based superconductors. Angle-resolved photoemission spectroscopy observed ‘‘replica bands' ' suggesting the importance of the interaction between FeSe electrons and STO phonons. These facts rejuvenated the quest for T_c enhancement mechanisms in iron-based, especially ironchalcogenide, superconductors. Here, we perform the first numerically-exact sign-problem-free quantum Monte Carlo simulations to iron-based superconductors. We(1) study the electronic pairing mechanism intrinsic to heavily electron doped FeSe films, and(2) examine the effects of electron–phonon interaction between FeSe and STO as well as nematic fluctuations on T_c. Armed with these results, we return to the question ‘‘what makes the Tcof monolayer FeSe on SrTiO_3 so high?'' in the conclusion and discussions.
基金supported by Beijing Natural Science Foundation (Grant No.Z200005)the National Key Research and Development Program of China (Grant No.2021YFA1401800)the National Natural Science Foundation of China (Grant Nos.52272267 and 52202342)。
文摘The rattling mode,an anharmonic vibrational phonon,is widely recognized as a critical factor in the emergence of superconductivity in caged materials.Here,we present a counterexample in a filled-skutterudite superconductor Ba_(x)Ir_(4)Sb_(12)(x=0.8,0.9,1.0),synthesized via a high-pressure route.Transport measurements down to liquid 3He temperatures reveal a transition temperature(T_(c))of 1.2 K and an upper critical field(H_(c2))of 1.3 T.Unlike other superconductors with caged structures,the Ba_(x)Ir_(4)Sb_(12)(X=P,As,Sb)family exhibits a monotonic decreasing T_(c) with the enhancement of the rattling mode,as indicated by fitting the Bloch–Grüneisen formula.Theoretical analysis suggests that electron doping from Ba transforms the direct bandgap IrSb3 into a metal,with the Fermi surface dominated by the hybridization of Ir 5d and Sb 5p orbitals.Our findings of decoupled rattling modes and superconductivity distinguish the Ba_(x)Ir_(4)Sb_(12) family from other caged superconductors,warranting further exploration into the underlying mechanism.
文摘Electron density differences resulting from atom displacement patterns aligned with phonon modes in MgB2 have been calculated using density functional theory (DFT). The extent of phonon anomalies, identified as indicators of the superconducting transition temperature, Tc, under a range of conditions in AlB2-type structures, reduce as boron atoms are displaced from their equilibrium positions along E2g mode directions. The Fermi energy for displacements along the directions of the E2g phonon mode accounts for changes in the covalent B-B bond electronic charge density. We applied differential atom displacements to show that the shifted σ band structure associated with the light effective mass became tangential to the Fermi level and that the Fermi surface undergoes a topological transition at a critical relative displacement of ~0.6% of the boron atoms from equilibrium. The difference in Fermi energies at this critical displacement and at the equilibrium position correspond to the superconducting energy gap. The net volume between tubular σ surfaces in reciprocal space correlated with the depth of the phonon anomaly and, by inference, it is a key to an understanding of superconductivity. This ab initioapproach offers a phenomenological understanding of the factors that determine Tc based on knowledge of the crystal structure.
基金The NNSF (10071067) the Nature Science Foundation of Jiangsu Province, China.
文摘This paper is concerned with the minimization problem related to the superconductivity with thermal noise. We study the asymptotic behavior of the minimizes of this problem as the parameters tending to zero and prove the vortices-pinning mechanism.
文摘Studying the complexity of the electronic phase diagram is at the heart of understanding strongly correlated system in general,with high Tc superconductors as the most known examples.High temperature superconductivity has a wide range of application potentials in power transmission,nuclear magnetic resonance,magnetic levitation transportation,aerospace,information and communication technologies,etc.Understanding its mechanism remains a long-standing challenge,due to its complex material structures and interlays among different phases such as charge density wave,antiferromagnetic and superconducting phases.As a result,this has greatly hindered its further development.
文摘For the superconductors(Rb_xK_(1-x))_3C_(60)(x=0.1),according to BCS theory and assuming that the virtual phonon acting on electron-pair is corresponding to the intrasolecular vibration in the bnckminnterfullerene C_(60),a linear relationship of the superconducting transition temperature T_c with x has been derived,which is in agreement with the experimentals,
基金by the National Key R&D Program of China(Grant No.2017YFA0302902)。
文摘It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces,characterized by a nonintegrable phase factor that an elementary particle of charge q acquires from A to B points:P exp(iq/hc∫A^(B)A_(μ)dxμ),where Aμis the gauge potential and P stands for path ordering.In a many-body system of strongly correlated electrons,if the so-called Mott gap is opened up by interaction,the corresponding Hilbert space will be fundamentally changed.A novel nonintegrable phase factor known as phase-string will appear and replace the conventional Fermi statistics to dictate the low-lying physics.Protected by the Mott gap,which is clearly identified in the high-Tc cuprate with a magnitude>1.5 e V,such a singular phase factor can enforce a fractionalization of the electrons,leading to a dual world of exotic elementary particles with a topological gauge structure.A non-Fermi-liquid“parent”state will emerge,in which the gapless Landau quasiparticle is only partially robust around the so-called Fermi arc regions,while the main dynamics are dominated by two types of gapped spinons.Antiferromagnetism,superconductivity,and a Fermi liquid with full Fermi surface can be regarded as the low-temperature instabilities of this new parent state.Both numerics and experiments provide direct evidence for such an emergent physics of the Mottness,which lies in the core of a high-Tc superconducting mechanism.
