Dy$_{2}$Zr$_{2}$O$_{7}$ a disordered pyrochlore system, exhibits the spin ice freezing under the application of magnetic field. Our studies suggest the stabilization of pyrochlore phase in Dy$_{2-x}$La$_{x}$Zr$_{2}$O$_{7}$ with the substitution of nonmagnetic La, along with the biphasic mixture for the intermediate compositions. We observed that the higher La compositions (1.5 $\leq$ x $\leq$ 1.9), show spin freezing (T $\sim$ 17 K) similar to the field induced spin ice freezing for low La compositions (0 $\leq$ x $\leq$ 0.5), and the well known spin ice systems Dy$_{2}$Ti$_{2}$O$_{7}$ and Ho$_{2}$Ti$_{2}$O$_{7}$. The low temperature magnetic state for higher La compositions (1.5 $\leq$ x $\leq$ 1.9) culminates into spin glass state below 6 K. The Cole-Cole plot and Casimir-du Pr$\acute{e}$ fit shows narrow distribution of spin relaxation time in these compounds.
Spin ice materials are the model systems that have a zero-point entropy as \textit{T} $\rightarrow$ 0 K, owing to the frozen disordered states. Here, we chemically alter the well-known spin ice Ho$_{2}$Ti$_{2}$O$_{7}$ by replacing Ti sites with isovalent but larger Zr ion. Unlike the Ho$_{2}$Ti$_{2}$O$_{7}$ which is a pyrochlore material, Ho$_{2}$Zr$_{2}$O$_{7}$ crystallizes in disordered pyrochlore structure. We have performed detailed structural, ac magnetic susceptibility and heat capacity studies on Ho$_{2}$Zr$_{2}$O$_{7}$ to investigate the interplay of structural disorder and frustrated …
The structural, magnetic and Raman effect have been investigated on (Tb1-xEux)2Ti2O7. From structural study it is clear that Eu substitutes the Tb in Tb2Ti2O7. Raman effect study indicates the existence of hardening due to phonon-phonon anharmonic interaction. From dc-magnetic measurement it is observed that in Eu rich samples contribution of dipolar interaction is significant. From ac magnetic measurement of (Tb1-xEux)2Ti2O7 a new single ion weak spin freezing ~ 33K at zero magnetic field is observed. On applying a field of 1T, all the compounds show a field induced transition (T*) which shif…
We report results of muon spin relaxation and rotation ($μ$SR) experiments on the spin-liquid candidate~YbMgGaO$_{4}$. No static magnetism $\gtrsim 0.003μ_B$ per Yb ion, ordered or disordered, is observed down to 22~mK, a factor of two lower in temperature than previous measurements. Persistent (temperature-independent) spin dynamics are observed up to 0.20~K and at least 1~kOe, thus extending previous zero-field $μ$SR results over a substantial region of the $H$-$T$ phase diagram. Knight shift measurements in a 10-kOe transverse field reveal two lines with nearly equal amplitudes. Inhomogeneo…
We have performed a muon spin rotation study on polycrystalline samples of electron-doped layered manganites, La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ (0.4< x<1), in order to investigate the local magnetic structure and spin dynamics. Our results provide evidence for phase separation into A-type antiferromagnetic and charge-ordered phases for x=0.52 and spin freezing at low temperatures (T<100K) for 0.52<x<0.75. A new phase diagram which includes this spin freezing region is proposed.
We solve the orbitally degenerate two-band Hubbard model within dynamical mean field theory and map out the instabilities to various symmetry-broken phases based on an analysis of the corresponding lattice susceptibilities. Phase diagrams as a function of the Hund coupling parameter J are obtained both for the model with rotationally invariant interaction and for the model with Ising-type anisotropy. For negative J, an intra-orbital spin-singlet superconducting phase appears at low temperatures, while the normal state properties are characterized by an orbital freezing phenomenon. This is the …
Low temperature Spin freezing and Diffuse Magnetic Correlations in Tb$_{2}$Zr$_{2-x}$Ti$_{x}$O$_{7}$ (x = 0, 0.5)
Indian Institute of Technology Mandi（印度理工学院曼迪分校）；Heidelberg University（海德堡大学）；ISIS Neutron and Muon Source, STFC Rutherford Appleton Laboratory（STFC拉瑟福德阿普尔顿实验室ISIS中子与缪子源）；Center for Quantum Science and Technologies, Indian Institute of Technology Mandi（印度理工学院曼迪分校量子科学与技术中心）
We have studied the liquid - solid (L-S) phase transition of ^4He confined in nanoporous glass, which has interconnected nanopores of 2.5 nm in diameter. The L-S boundary is determined by the measurements of pressure and thermal response during slow cooling and warming. Below 1 K, the freezing pressure is elevated to 1.2 MPa from the bulk freezing pressure, and appears to be independent of temperature. The T-independent L-S boundary implies the existence of a localized Bose-Einstein condensation state, in which long-range superfluid coherence is destroyed by narrowness of the nanopores and ran…
We use $^{79}$Br nuclear quadrupole resonance (NQR) to demonstrate that ultra slow lattice dynamics set in below the temperature scale set by the Cu-Cu super-exchange interaction $J$~($\simeq160$~K) in the kagome lattice Heisenberg antiferromagnet Zn-barlowite. The lattice completely freezes below 50~K, and $^{79}$Br NQR lineshapes become twice broader due to increased lattice distortions. Moreover, the frozen lattice exhibits an oscillatory component in the transverse spin echo decay, a typical signature of pairing of nuclear spins by indirect nuclear spin-spin interaction. This indicates tha…
We investigate the phase diagram of the spin-orbit-coupled three orbital Hubbard model at arbitrary filling by means of dynamical mean-field theory combined with continuous-time quantum Monte Carlo. We find that the spin-freezing crossover occurring in the metallic phase of the non-relativistic multiorbital Hubbard model can be generalized to a $\mathbf{J}$-freezing crossover, with $\mathbf{J}=\mathbf{L}+\mathbf{S}$, in the spin-orbit-coupled case. In the $\mathbf{J}$-frozen regime the correlated electrons exhibit a non-trivial flavor selectivity and energy dependence. Furthermore, in the regi…
The high-temperature superconducting state in cuprates appears if charge carriers are doped into a Mott insulating parent compound. An unresolved puzzle is the unconventional nature of the normal state above the superconducting dome, and its connection to the superconducting instability. At weak hole-doping, a "pseudo-gap" metal state with signatures of time-reversal symmetry breaking is observed, which near optimal doping changes into a "strange metal" with non-Fermi liquid properties. Qualitatively similar phase diagrams are found in multi-orbital systems, such as pnictides, where the unconv…
We study the electronic properties of a LaEu0.20Sr0.15CuO4 single crystal under hydrostatic pressure up to 2.9 GPa. Both the freezing of the Cu 3d moments and the structural transition from the orthorhombic (LTO) to the tetragonal (LTT) phase are observed via the relaxation of the nuclear magnetization of La nuclei. Resistivity and magnetic susceptibility measurements have been carried out under pressure on the same sample. The combination of all data reveals the connection between glassy dynamics, charge localization and the disappearance of superconductivity in the LTT phase.
We report 17O NMR measurements in the S=1/2 Cu2+ kagome antiferromagnet Herbertsmithite ZnCu3(OH)6Cl2 down to 45mK in magnetic fields ranging from 2T to 12T. While Herbertsmithite displays a gapless spin-liquid behavior in zero field, we uncover an instability toward a spin-solid phase at sub-kelvin temperature induced by an applied magnetic field. The latter phase shows largely suppressed moments $\lesssim 0.1\muB$ and gapped excitations. The H-T phase diagram suggests the existence of a quantum critical point at the small but finite magnetic field mu0 Hc=1.55(25)T. We discuss this finding in…
The spinel oxides LiGaCr4O8 and LiInCr4O8 contain size-alternating pyrochlore lattices of spin-3/2 Cr3+ tetrahedra with different magnitudes of alternation. We show here that the solid solutions LiGa1-xInxCr4O8 between these two 'breathing' pyrochlore compounds display (i) rapid suppression of magnetic and structural transitions upon doping the end members, (ii) spin-glass-like freezing above 2 K in the range 0.1 $\lesssim$ x $\lesssim$ 0.6, and (iii) apparent spin-gap behavior for x $\gtrsim$ 0.7. Furthermore, no transitions are observed above 2 K at x ~ 0.9, where magnetic susceptibility rem…
Specific heat measurements in zero magnetic field are presented on a homologous series of geometrically frustrated, antiferromagnetic, Heisenberg garnet systems. Measurements of Gd3Ga5O12, grown with isotopically pure Gd, agree well with previous results on samples with naturally abundant Gd, showing no ordering features. In contrast, samples of Gd3Te2Li3O12 and Gd3Al5O12 are found to exhibit clear ordering transitions at 243 mK and 175 mK respectively. The effects of low level disorder are studied through dilution of Gd3+ with non-magnetic Y3+ in Gd3Te2Li3O12. A thorough structural characteri…
We study an unconventional two-dimensional, two-component classical plasma on a sphere, with emphasis on detecting signatures of melting transitions. This system is relevant to Ising-type quantum Hall states, and is unconventional in the sense that it features particles interacting via two different two-dimensional Coulomb interactions. One species of particles in the plasma carries charge of both types (Q_1,Q_2), while the other species carries only charge of the second type (0,-Q_2). We find signatures of a freezing transition at Q_1^2 approximately 140. This means that the species with char…
We report the results of magnetic measurements for the solid solution Ce$_2$Au$_{1-x}$Co$_x$Si$_3$. The results reveal that this solid solution is characterized by a magnetic phase diagram (plot of magnetic transition temperature versus $x$) unusual for Kondo lattices. In particular, the spin-glass freezing induced by disorder is observed only for the compositions at the weak coupling limit; as one approaches the quantum critical point by a gradual replacement of Au by Co, this disorder effect is surprisingly suppressed in favor of long range antiferro-magnetic ordering in contrast to expectat…
The structural phase diagram of the La1-xSrxMnO3 system in the compositional range 0.08 <= x <= 0.125 has been investigated by high-resolution synchrotron x-ray powder diffraction techniques between 20-600 K. Recent studies have reported that there is an unusual rentrant-type phase transition in this range involving an abrupt change in lattice parameters but no change in the crystal symmetry, which remains orthorhombic Pbnm. The transition to the reentrant phase is from a ferromagnetic metallic to a ferromagnetic insulating phase with some unusual properties. Our results demonstrate that for s…
We report the structural and magnetic properties of a new system LiRhMnO$_{4}$ (LRMO) through x-ray diffraction, bulk magnetization, heat capacity and $^{7}$Li nuclear magnetic resonance (NMR) measurements. LRMO crystallizes in the cubic space group $\mathit{Fd}$$\bar{3}$$\mathit{m}$. From the DC susceptibility data, we obtained the Curie-Weiss temperature $\mathrmθ_{\mathrm{CW}}$ = -26 K and Curie constant $\mathit{C}$ = 1.79 Kcm$^{3}$/mol suggesting antiferromagnetic correlations among the magnetic Mn$^{4+}$ ions with an effective spin $\mathit{S}$ = $\frac{3}{2}$. At $\mathit{H}$ = 50 Oe, t…
An antiferromagnetic Hund coupling in multiorbital Hubbard systems induces orbital freezing and an associated superconducting instability, as well as unique composite orders in the case of an odd number of orbitals. While the rich phase diagram of the half-filled three-orbital model has recently been explored in detail, the properties of the doped system remain to be clarified. Here, we complement the previous studies by computing the entropy of the half-filled model, which exhibits an increase in the orbital-frozen region, and a suppression in the composite ordered phase. The doping dependent…
The robustness of spin liquids with respect to small perturbations, and the way magnetic frustration can be lifted by slight changes in the balance between competing magnetic interactions remains a rich and open issue. We address this question through the study of the Gadolinium Aluminium garnet Gd$_3$Al$_5$O$_{12}$, a related compound to the extensively studied Gd$_3$Ga$_5$O$_{12}$. We report on its magnetic properties at very low temperature. We show that despite a freezing at about 300 mK, no magnetic transition is observed, suggesting the presence of a spin liquid state down to the lowest …
We have investigated the structural and magnetic transitions in CsCoO$_2$ using calorimetric measurements, neutron powder diffraction (NPD), density functional theory (DFT) calculations and muon-spin relaxation ($μ$SR) measurements. CsCoO$_2$ exhibits three-dimensional long-range antiferromagnetic (AFM) order at 424~K, resulting in antiferromagnetic alignment of chains of ferromagnetically ordered Co-Co spin dimers. Although there is no change in magnetic structure around a structural transition at $T^{*}=100$~K, the resulting bifurcation of corner-shared Co--O--Co bond angles causes a weakeni…
Ba$_3$Mn$_2$O$_8$ is a geometrically frustrated spin dimer compound. We investigate the effect of site disorder on the zero field phase diagram of this material by considering the solid solution Ba$_{3}$(Mn$_{1-x}$V$_{x}$)$_{2}$O$_{8}$, where nonmagnetic V$^{5+}$ ions partially substitute magnetic Mn$^{5+}$ ions. This substitution results in unpaired $S=1$ moments for half-substituted dimers, which are ungapped and therefore susceptible to types of magnetic order not present in the parent compound. AC susceptibility measurements of compositions between $x=0.046$ and $x=0.84$ show a sharp frequ…
MoTe2 is a rare transition-metal ditelluride having two kinds of layered polytypes, hexagonal structure with trigonal prismatic Mo coordination and monoclinic structure with octahedral Mo coordination. The monoclinic distortion in the latter is caused by anisotropic metal-metal bonding. In this work, we have examined the Nb doping effect on both polytypes of MoTe2 and clarified a structural phase diagram for Mo1-xNbxTe2 containing four kinds of polytypes. A rhombohedral polytype crystallizing in polar space group has been newly identified as a high-temperature metastable phase at slightly Nb-r…
We have investigated the electronic properties of SrFe$_2$(As$_{1-x}$P$_x$)$_2$ ($0\leqq x\leqq1$) single crystals with postannealing treatment and established a phase diagram of this system. The postannealing treatment reduced the residual resistivity in an antiferromagnetic-orthorhombic phase and enhanced the superconducting transition temperature to $T_{c, optimal}$=33\,K in the superconducting phase. The obtained phase diagram and electronic properties are similar to those of BaFe$_2$(As$_{1-x}$P$_x$)$_2$ despite the large difference in lattice constants. This indicates that, for supercond…
In addition to its promising potential for applications, GaV4S8 shows very interesting physical properties with temperature and magnetic field. These properties can be tuned by applying hydrostatic pressure in order to reveal and understand the physics of these materials. Not only pressure induces an insulator-to-metal transition in GaV4S8 but it also has an interesting effect on the structural and magnetic transitions. Using a combination of AC calorimetry, capacitance, and resistivity measurements under pressure, we determine the evolution of the structural and magnetic transitions with pres…
We use neutron scattering to study the structural and magnetic phase transitions in the iron pnictides CeFeAsO1-xFx as the system is tuned from a semimetal to a high-transition-temperature (high-Tc) superconductor through Fluorine (F) doping x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a stripe like commensurate antiferromagnetic order with decreasing temperature. With increasing Fluorine doping, the structural phase transition decreases gradually while the antiferromagnetic order is suppressed before the appearance of superconductivity, resulting an el…
Tetrahedrally ferromagnetic correlations and a glassy-freezing anomaly in the breathing pyrochlore magnet $\mathrm{AgInCr_4S_8}$ with partial $A$-site disorder
Tokyo University of Agriculture and Technology（东京农工大学）；The Institute for Solid State Physics, The University of Tokyo（东京大学固体物理研究所）；Kyoto University（京都大学）
A full implementation of the $ab$ $initio$ density functional plus dynamical mean field theory (DFT+DMFT) formalism to perform total energy calculations and structural relaxations is proposed and implemented. The method is applied to the structural and metal-insulator transitions of the rare earth nickelate perovskites as a function of rare earth ion, pressure, and temperature. In contrast to previous DFT and DFT+$U$ theories, the present method accounts for the experimentally observed structure of $La$NiO$_3$ and the insulating nature of the other perovskites, and quantitatively reproduces th…
The quasi-skutterudite superconductor Sr$_3$Rh$_4$Sn$_{13}$ features a pronounced anomaly in electrical resistivity at $T^*\sim$138 K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centred around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of $T^*$ as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at …
Several observed transport and thermodynamic properties of the heavy-fermion compound YbRh2Si2 in the quantum critical regime are unusual and suggest that the fermionic quasiparticles are critical, characterized by a scale-dependent diverging effective mass. A theory based on the concept of critical quasiparticles (CQP) scattering off antiferromagnetic spin fluctuations in a strong-coupling regime has been shown to successfully explain the unusual existing data and to predict a number of so far unobserved properties. In this paper, we point out a new feature of a magnetic field-tuned quantum c…
Single-crystal structural phase diagram of stoichiometric bilayer nickelate La3Ni2O7 under hydrostatic pressure
The University of Tokyo（东京大学）；RIKEN Center for Emergent Matter Science (CEMS)（理化学研究所 新兴物质科学中心）；Tohoku University（东北大学）；Japan Synchrotron Radiation Research Institute (JASRI)（日本同步辐射研究所）；Tokyo College, The University of Tokyo（东京大学东京学院）；Institute of Engineering Innovation, The University of Tokyo（东京大学工程创新研究所）；RIKEN Pioneering Research Institute (PRI)（理化学研究所 先驱研究 institute）
We report that the 122 type Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ solid solution undergoes an anomalous structural transition from the uncollapsed to the collapsed ThCr$_2$Si$_2$ structure at a distinct onset composition near $x=0.5$. Correlated with the structural changes, the electronic system evolves from a nearly ferromagnetic Fermi liquid to an antiferromagnetic metal, through a complex crossover regime. The structural collapse, driven by P-P bonding across the (Sr,Ca) layers, is much more pronounced in this system than it is in the analogous Fe-based system, indicating a strong sensitivity of stru…
