15 research outputs found
Colossal c-axis response and lack of rotational symmetry breaking within the kagome plane of the CsVSb superconductor
The kagome materials AV4Sb (A = K, Rb, Cs) host an intriguing
interplay between unconventional superconductivity and charge-density-waves.
Here, we investigate CsVSb by combining high-resolution
thermal-expansion, heat-capacity and electrical resistance under strain
measurements. We directly unveil that the superconducting and charge-ordered
states strongly compete, and that this competition is dramatically influenced
by tuning the crystallographic c-axis. In addition, we report the absence of
additional bulk phase transitions within the charge-ordered state, notably
associated with rotational symmetry-breaking within the kagome planes. This
suggests that any breaking of the C invariance occurs via different
stacking of C-symmetric kagome patterns. Finally, we find that the
charge-density-wave phase exhibits an enhanced A-symmetric
elastoresistance coefficient, whose large increase at low temperature is driven
by electronic degrees of freedom
Charge density wave transitions, soft phonon, and possible electronic nematicity in BaNi₂(As₁₋ₓPₓ)₂
A detailed investigation of BaNi2(As1−xPx)2 single crystals using high-resolution thermal-expansion, heat-capacity, Young\u27s-modulus, and resistivity measurements is presented. The phase diagram of BaNi2(As1−xPx)2 is shown to be much richer than suggested by the original data of Kudo et al. [Phys. Rev. Lett. 109, 097002 (2012)]. The transition to the commensurate charge density wave (C-CDW) is always preceded by a fourfold symmetry-breaking transition associated with the long-range ordering of a strongly fluctuating unidirectional incommensurate charge density wave (I-CDW). Significant precursors above the I-CDW and C-CDW transitions are seen in the thermal expansion and resistivity and are particularly evident in the temperature dependence of the c/a ratio of the lattice parameters. Heat-capacity measurements of the crystals with a higher P content and a higher critical temperature of 3.2 K uncover a Debye-like behavior of a soft-phonon mode with a very low ΘDebye of roughly 50 K. Associated with this soft phonon are unusually large thermal-expansion anomalies, resulting in logarithmically diverging uniaxial phonon Grüneisen parameters. Young\u27s-modulus data of these higher-Tc crystals exhibit a significant softening in both B1g and B2g channels, which is argued to be incompatible with nematic criticality and is rather associated with a broad phase transition to an hitherto unknown structure. Possible origins of the increase in the superconducting critical temperature with P substitution are discussed
Precursor region with full phonon softening above the charge-density-wave phase transition in 2H-TaSe2
Research on charge-density-wave (CDW) ordered transition-metal dichalcogenides continues to unravel new states of quantum matter correlated to the intertwined lattice and electronic degrees of freedom. Here, we report an inelastic x-ray scattering investigation of the lattice dynamics of the canonical CDW compound 2H-TaSe2 complemented by angle-resolved photoemission spectroscopy and density functional perturbation theory. Our results rule out the formation of a central-peak without full phonon softening for the CDW transition in 2H-TaSe2 and provide evidence for a novel precursor region above the CDW transition temperature TCDW, which is characterized by an overdamped phonon mode and not detectable in our photoemission experiments. Thus, 2H-TaSe2 exhibits structural before electronic static order and emphasizes the important lattice contribution to CDW transitions. Our ab-initio calculations explain the interplay of electron-phonon coupling and Fermi surface topology triggering the CDW phase transition and predict that the CDW soft phonon mode promotes emergent superconductivity near the pressure-driven CDW quantum critical point
An electronic nematic liquid in BaNiAs
Understanding the organizing principles of interacting electrons and the emergence of novel electronic phases is a central endeavor of condensed matter physics. Electronic nematicity, in which the discrete rotational symmetry in the electron fluid is broken while the translational one remains unaffected, is a prominent example of such a phase. It has proven ubiquitous in correlated electron systems, and is of prime importance to understand Fe-based superconductors. Here, we find that fluctuations of such broken symmetry are exceptionally strong over an extended temperature range above phase transitions in BaNi(AsP), the nickel homologue to the Fe-based systems. This lends support to a type of electronic nematicity, dynamical in nature, which exhibits a particularly strong coupling to the underlying crystal lattice. Fluctuations between degenerate nematic configurations cause splitting of phonon lines, without lifting degeneracies nor breaking symmetries, akin to spin liquids in magnetic systems
Strain-Tuning of 2D and 3D Charge-Density Waves in High-Temperature Superconducting YBaCuO
Uniaxial pressure experiments in underdoped YBaCuO
provide an efficient approach to the control of the competition between
charge-density waves (CDWs) and superconductivity. It can enhance the
correlation volume of ubiquitous short-range CDW correlations and above a
critical value, even induce a long-range CDW order otherwise only accessible
through the suppression of superconductivity by large magnetic fields. Here we
use x-ray diffraction with access to large areas of reciprocal space to study
the evolution of long- and short-range CDWs with in-plane strains and as a
function of doping. This further allows us to precisely monitor in-situ the
structural changes induced by uniaxial pressurization of the crystals for a
precise strain estimation in measurements up to compression.
Interestingly, we uncover direct evidence for a competition between long- and
short-range CDWs and show that the long-range CDW modulation remains
incommensurate at all investigated strains and temperatures, showing neither
signs of discommensurations nor a pair-density wave component at
below . We discuss the impact
of structural disorder and the relationship of our findings to previous reports
on nematicity in high-temperature superconducting cuprates. More generally, our
results underscore the potential of strain tuning as a powerful tool for
probing and manipulating competing orders in quantum materials.Comment: I. Vinograd and S. M. Souliou contributed equally to this wor
High field charge order across the phase diagram of YBa₂Cu₃Oy
In hole-doped cuprates there is now compelling evidence that inside the pseudogap phase, charge order breaks translational symmetry. In YBa2Cu3O y charge order emerges in two steps: a 2D order found at zero field and at high temperature inside the pseudogap phase, and a 3D order that is superimposed below the superconducting transition Tc when superconductivity is weakened by a magnetic field. Several issues still need to be addressed such as the effect of disorder, the relationship between those charge orders and their respective impact on the Fermi surface. Here, we report high magnetic field sound velocity measurements of the 3D charge order in underdoped YBa2Cu3O y in a large doping range. We found that the 3D charge order exists over the same doping range as its 2D counterpart, indicating an intimate connection between the two distinct orders. Moreover, our data suggest that 3D charge order has only a limited impact on low-lying electronic states of YBa2Cu3O y
Hidden magnetism at the pseudogap critical point of a high temperature superconductor
The mysterious pseudogap phase of cuprate superconductors ends at a critical
hole doping level p* but the nature of the ground state below p* is still
debated. Here, we show that the genuine nature of the magnetic ground state in
La2-xSrxCuO4 is hidden by competing effects from superconductivity: applying
intense magnetic fields to quench superconductivity, we uncover the presence of
glassy antiferromagnetic order up to the pseudogap boundary p* ~ 0.19, and not
above. There is thus a quantum phase transition at p*, which is likely to
underlie highfield observations of a fundamental change in electronic
properties across p*. Furthermore, the continuous presence of quasi-static
moments from the insulator up to p* suggests that the physics of the doped Mott
insulator is relevant through the entire pseudogap regime and might be more
fundamentally driving the transition at p* than just spin or charge ordering.Comment: 26 pages, supplementary info include
Ultrasound studies of the normal state of high temperature cuprates superconductors
Dans les cuprates, des oxydes de cuivre, une supraconductivité non conventionnelle, confinée entre isolant de Mott et liquide de Fermi corrélé, apparaît par dopage chimique en porteurs de charges. Au-delà de la supraconductivité, le diagramme de phase renferme de nombreux ordres électroniques, notamment des ordres de charges et spins, qui interagissent entre eux mais également avec la supraconductivité. Une connaissance profonde de ce diagramme de phase est une étape nécessaire à la résolution de l'énigme de la supraconductivité des cuprates. Pour cela on propose ici une étude de la vitesse et de l'atténuation du son, une fois la supraconductivité affaiblie jusqu'à basse température par des champs magnétiques intenses.La première (et principale) partie de cette thèse s'intéresse au magnétisme de La2-xSrxCuO4(LSCO). Dans ce composé un verre antiferromagnétique est en forte compétition avec la supraconductivité. L'établissement de signatures ultrasonores associées à cet ordre a permis une étude en champs magnétiques pulsés, jusqu'à environ 90 T, qui indique qu'alors il persiste jusqu'à un dopage qui semble coïncider avec celui de la disparition du pseudogap, p*. L'existence de moments magnétiques quasi-statiques en champs magnétiques intenses suggère que les signatures de criticalités quantiques, mais également la chute du nombre de Hall, observées dans certains cuprates dans des conditions similaires, à p*, pourraient être liées au verre antiferromagnétique plutôt qu'au pseudogap lui-même.Dans une courte seconde partie, on s'intéresse aux deux ordres de charges, 2D et 3D, de YBa2Cu3O6+δ (Y-123) : une problématique distincte mais reliée à la précédente. Une étude systématique en dopage de la vitesse du son dans Y-123 restreint le domaine d'existence de l'ordre de charge 3D et indique que ce dernier est peu probablement à l'origine de la reconstruction de la surface de Fermi observée dans ce composé. La susceptibilité à une déformation élastique de la température critique supraconductrice, dTc/dεi, obtenue également par vitesse du son, interroge quant à elle sur la possibilité d'un scénario dans lequel sa dépendance en dopage - complexe et anisotrope - s'explique uniquement par une compétition entre supraconductivité et ordre(s) de charge(s).In cuprates, copper oxides, an unconventionnal superconductivity appears by chemical doping between a Mott insulator and a correlated Fermi liquid. Beyond superconductivity, the phase diagram includes multiple broken symmetry phases, including spin and charge density waves. All these phases interact together and with superconductivity, in a complex way. A deeper knowledge of this phase diagram is without doubt a necessary step toward the resolution of the high-Tc enigma. In this aim, we propose in this experimental thesis to measure velocity and attenuation of sound in the low temperature normal state of cuprates, using high magnetic fields.The first (main) part of this thesis focus on the magnetism of La2-xSrxCuO4 (LSCO). In this compound, an antiferromagnetic glass competes with superconductivity. By applying high magnetic fields of the order of 90 T we show that, when superconductivity is weakened enough, the antiferromagnetic glass disappears together with the pseudogap. The persistence of this order up to p*, and the associated ordered magnetic moment, could explain recent observations at p* without necessarily implying that the pseudogap is an ordered phase. Among them are the fall of the Hall number and quantum criticality signatures observed in different cuprates.The shorter second part deals with a related topic: the two distinct charge density waves (CDW, 2D and 3D) of YBa2Cu3O6+_ (Y-123). By performing sound velocity measurements in high magnetic fields we constrain the doping range of the 3D CDW and show that the latter is unlikely at the origin of the Fermi surface reconstruction. Sound velocity measurements also allow the determination of dTc/dεi, the Tc's susceptibility to a given elastic deformation. The complex and anisotropic doping dependence of dTc/dεi cannot be easily reconcile alone with a scenario of competition between CDW(s) and superconductivity
Etudes ultrasonores de l'état normal des cuprates supraconducteurs à haute température critique
In cuprates, copper oxides, an unconventionnal superconductivity appears by chemical doping between a Mott insulator and a correlated Fermi liquid. Beyond superconductivity, the phase diagram includes multiple broken symmetry phases, including spin and charge density waves. All these phases interact together and with superconductivity, in a complex way. A deeper knowledge of this phase diagram is without doubt a necessary step toward the resolution of the high-Tc enigma. In this aim, we propose in this experimental thesis to measure velocity and attenuation of sound in the low temperature normal state of cuprates, using high magnetic fields.The first (main) part of this thesis focus on the magnetism of La2-xSrxCuO4 (LSCO). In this compound, an antiferromagnetic glass competes with superconductivity. By applying high magnetic fields of the order of 90 T we show that, when superconductivity is weakened enough, the antiferromagnetic glass disappears together with the pseudogap. The persistence of this order up to p*, and the associated ordered magnetic moment, could explain recent observations at p* without necessarily implying that the pseudogap is an ordered phase. Among them are the fall of the Hall number and quantum criticality signatures observed in different cuprates.The shorter second part deals with a related topic: the two distinct charge density waves (CDW, 2D and 3D) of YBa2Cu3O6+_ (Y-123). By performing sound velocity measurements in high magnetic fields we constrain the doping range of the 3D CDW and show that the latter is unlikely at the origin of the Fermi surface reconstruction. Sound velocity measurements also allow the determination of dTc/dεi, the Tc's susceptibility to a given elastic deformation. The complex and anisotropic doping dependence of dTc/dεi cannot be easily reconcile alone with a scenario of competition between CDW(s) and superconductivity.Dans les cuprates, des oxydes de cuivre, une supraconductivité non conventionnelle, confinée entre isolant de Mott et liquide de Fermi corrélé, apparaît par dopage chimique en porteurs de charges. Au-delà de la supraconductivité, le diagramme de phase renferme de nombreux ordres électroniques, notamment des ordres de charges et spins, qui interagissent entre eux mais également avec la supraconductivité. Une connaissance profonde de ce diagramme de phase est une étape nécessaire à la résolution de l'énigme de la supraconductivité des cuprates. Pour cela on propose ici une étude de la vitesse et de l'atténuation du son, une fois la supraconductivité affaiblie jusqu'à basse température par des champs magnétiques intenses.La première (et principale) partie de cette thèse s'intéresse au magnétisme de La2-xSrxCuO4(LSCO). Dans ce composé un verre antiferromagnétique est en forte compétition avec la supraconductivité. L'établissement de signatures ultrasonores associées à cet ordre a permis une étude en champs magnétiques pulsés, jusqu'à environ 90 T, qui indique qu'alors il persiste jusqu'à un dopage qui semble coïncider avec celui de la disparition du pseudogap, p*. L'existence de moments magnétiques quasi-statiques en champs magnétiques intenses suggère que les signatures de criticalités quantiques, mais également la chute du nombre de Hall, observées dans certains cuprates dans des conditions similaires, à p*, pourraient être liées au verre antiferromagnétique plutôt qu'au pseudogap lui-même.Dans une courte seconde partie, on s'intéresse aux deux ordres de charges, 2D et 3D, de YBa2Cu3O6+δ (Y-123) : une problématique distincte mais reliée à la précédente. Une étude systématique en dopage de la vitesse du son dans Y-123 restreint le domaine d'existence de l'ordre de charge 3D et indique que ce dernier est peu probablement à l'origine de la reconstruction de la surface de Fermi observée dans ce composé. La susceptibilité à une déformation élastique de la température critique supraconductrice, dTc/dεi, obtenue également par vitesse du son, interroge quant à elle sur la possibilité d'un scénario dans lequel sa dépendance en dopage - complexe et anisotrope - s'explique uniquement par une compétition entre supraconductivité et ordre(s) de charge(s)
Etudes ultrasonores de l'état normal des cuprates supraconducteurs à haute température critique
In cuprates, copper oxides, an unconventionnal superconductivity appears by chemical doping between a Mott insulator and a correlated Fermi liquid. Beyond superconductivity, the phase diagram includes multiple broken symmetry phases, including spin and charge density waves. All these phases interact together and with superconductivity, in a complex way. A deeper knowledge of this phase diagram is without doubt a necessary step toward the resolution of the high-Tc enigma. In this aim, we propose in this experimental thesis to measure velocity and attenuation of sound in the low temperature normal state of cuprates, using high magnetic fields.The first (main) part of this thesis focus on the magnetism of La2-xSrxCuO4 (LSCO). In this compound, an antiferromagnetic glass competes with superconductivity. By applying high magnetic fields of the order of 90 T we show that, when superconductivity is weakened enough, the antiferromagnetic glass disappears together with the pseudogap. The persistence of this order up to p*, and the associated ordered magnetic moment, could explain recent observations at p* without necessarily implying that the pseudogap is an ordered phase. Among them are the fall of the Hall number and quantum criticality signatures observed in different cuprates.The shorter second part deals with a related topic: the two distinct charge density waves (CDW, 2D and 3D) of YBa2Cu3O6+_ (Y-123). By performing sound velocity measurements in high magnetic fields we constrain the doping range of the 3D CDW and show that the latter is unlikely at the origin of the Fermi surface reconstruction. Sound velocity measurements also allow the determination of dTc/dεi, the Tc's susceptibility to a given elastic deformation. The complex and anisotropic doping dependence of dTc/dεi cannot be easily reconcile alone with a scenario of competition between CDW(s) and superconductivity.Dans les cuprates, des oxydes de cuivre, une supraconductivité non conventionnelle, confinée entre isolant de Mott et liquide de Fermi corrélé, apparaît par dopage chimique en porteurs de charges. Au-delà de la supraconductivité, le diagramme de phase renferme de nombreux ordres électroniques, notamment des ordres de charges et spins, qui interagissent entre eux mais également avec la supraconductivité. Une connaissance profonde de ce diagramme de phase est une étape nécessaire à la résolution de l'énigme de la supraconductivité des cuprates. Pour cela on propose ici une étude de la vitesse et de l'atténuation du son, une fois la supraconductivité affaiblie jusqu'à basse température par des champs magnétiques intenses.La première (et principale) partie de cette thèse s'intéresse au magnétisme de La2-xSrxCuO4(LSCO). Dans ce composé un verre antiferromagnétique est en forte compétition avec la supraconductivité. L'établissement de signatures ultrasonores associées à cet ordre a permis une étude en champs magnétiques pulsés, jusqu'à environ 90 T, qui indique qu'alors il persiste jusqu'à un dopage qui semble coïncider avec celui de la disparition du pseudogap, p*. L'existence de moments magnétiques quasi-statiques en champs magnétiques intenses suggère que les signatures de criticalités quantiques, mais également la chute du nombre de Hall, observées dans certains cuprates dans des conditions similaires, à p*, pourraient être liées au verre antiferromagnétique plutôt qu'au pseudogap lui-même.Dans une courte seconde partie, on s'intéresse aux deux ordres de charges, 2D et 3D, de YBa2Cu3O6+δ (Y-123) : une problématique distincte mais reliée à la précédente. Une étude systématique en dopage de la vitesse du son dans Y-123 restreint le domaine d'existence de l'ordre de charge 3D et indique que ce dernier est peu probablement à l'origine de la reconstruction de la surface de Fermi observée dans ce composé. La susceptibilité à une déformation élastique de la température critique supraconductrice, dTc/dεi, obtenue également par vitesse du son, interroge quant à elle sur la possibilité d'un scénario dans lequel sa dépendance en dopage - complexe et anisotrope - s'explique uniquement par une compétition entre supraconductivité et ordre(s) de charge(s)