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We investigate partially disordered antiferromagnetism in ${\mathrm{CoCl}}_{2}$-2SC(${\mathrm{NH}}_{2}$)${}_{2}$, in which $ab$-plane hexagonal layers are staggered along the $c$ axis rather than stacked. A robust 1/3 state forms in applied magnetic fields in which the spins are locked, varying as a function of neither temperature nor field. By contrast, in zero field and applied fields at higher temperatures, partial antiferromagnetic order occurs, in which free spins are available to create a Curie-like magnetic susceptibility. We report measurements of the crystallographic structure and the specific heat, magnetization, and electric polarization down to $T=50\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$ and up to ${\ensuremath{\mu}}_{0}H=60\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. The ${\mathrm{Co}}^{2+}\phantom{\rule{4pt}{0ex}}\mathbf{S}=3/2$ spins are Ising-like and form distorted hexagonal layers. The Ising energy scale is well separated from the magnetic exchange, and both energy scales are accessible to the measurements, allowing us to cleanly parametrize them. In transverse fields, a quantum Ising phase transition can be observed at 2 T. Finally, we find that magnetic exchange striction induces changes in the electric polarization up to $3\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$, and single-ion magnetic anisotropy effects induce a much larger electric polarization change of $300\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$.

The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation (BEC) and superfluidity, which have been tested experimentally in a variety of different systems. When bosons are interacting, disorder can destroy condensation leading to a so-called Bose glass. This phase has been very elusive to experiments due to the absence of any broken symmetry and of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (Br-doped dichloro-tetrakis-thiourea-Nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand-canonical ensemble; Br-doping introduces disorder in the hoppings and interaction strengths, leading to localization of the bosons into a Bose glass down to zero field, where it acquires the nature of an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the BEC (corresponding to a magnetically ordered phase) is marked by a novel, universal exponent governing the scaling on the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents the first, quantitative account of the universal features of disordered bosons in the grand-canonical ensemble., Comment: 13+6 pages, 5+6 figures; v2: Fig. 5 updated

Inhomogeneous electronic states resulting from entangled spin, charge, and lattice degrees of freedom are hallmarks of strongly correlated electron materials; such behavior has been observed in many classes of d-electron materials, including the high-Tc copper-oxide superconductors, manganites, and most recently the iron-pnictide superconductors. The complexity generated by competing phases in these materials constitutes a considerable theoretical challenge-one that still defies a complete description. Here, we report a new manifestation of electronic inhomogeneity in a strongly correlated f-electron system, using CeCoIn5 as an example. A thermodynamic analysis of its superconductivity, combined with nuclear quadrupole resonance measurements, shows that nonmagnetic impurities (Y, La, Yb, Th, Hg and Sn) locally suppress unconventional superconductivity, generating an inhomogeneous electronic "Swiss cheese" due to disrupted periodicity of the Kondo lattice. Our analysis may be generalized to include related systems, suggesting that electronic inhomogeneity should be considered broadly in Kondo lattice materials., Comment: 27 pages

The heavy-fermion superconductor CeCoIn5 is the first material, where different experimental probes show strong evidence pointing to the realization of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The inhomogeneous superconducting FFLO state with a periodically modulated order parameter was predicted to appear in Pauli-limited, sufficiently clean type-II superconductors already more than 40 years ago. On the other hand, CeCoIn5 is supposed to be close to a magnetic quantum critical point (QCP) showing strong antiferromagnetic (AFM) spin fluctuations (SF) at atmospheric pressure. We studied the evolution of the FFLO phase away from the influence of the strong AFM-SF by heat capacity experiments under pressure (0 GPa

The heavy-fermion superconductor CeCoIn 5 is the first material, where different experimental probes show strong evidence pointing to the realization of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state. The inhomogeneous superconducting FFLO state with a periodically modulated order parameter was predicted to appear in Pauli-limited, sufficiently clean type-II superconductors already more than 40 years ago. On the other hand, CeCoIn 5 is supposed to be close to a magnetic quantum critical point (QCP) showing strong antiferromagnetic (AFM) spin fluctuations (SF) at atmospheric pressure. We studied the evolution of the FFLO phase away from the influence of the strong AFM-SF by heat capacity experiments under pressure (0 GPa ≤ P ≤1.5 GPa, 0 T ≤µ 0 H ≤14 T, and 100 mK ≤ T ≤4 K). Our results prove the stability of the the FFLO phase under pressure. It even expands, while the Pauli-limiting becomes weaker and the AFM-SF are suppressed. This shows the intriguing influence of the AFM-SF on the FFLO state.

We present experimental results for the heavy-electron compound CeCu$_{4}$Ga which show that it possesses short-range magnetic correlations down to a temperature of $T = 0.1$ K. Our neutron scattering data show no evidence of long-range magnetic order occurring despite a peak in the specific heat at $T^{*} =1.2$ K. Rather, magnetic diffuse scattering occurs which corresponds to short-range magnetic correlations occurring across two unit cells. The specific heat remains large as $T\sim0$ K resulting in a Sommerfeld coefficient of $\gamma_{0} = 1.44(2)$ J/mol-K$^{2}$, and, below $T^{*}$, the resistivity follows $T^{2}$ behavior and the ac magnetic susceptibility becomes temperature independent. A magnetic peak centered at an energy transfer of $E_{\rm{c}}=0.24(1)$ meV is seen in inelastic neutron scattering data which shifts to higher energies and broadens under a magnetic field. We discuss the coexistence of large specific heat, magnetic fluctuations, and short-range magnetic correlations at low temperatures and compare our results to those for materials possessing spin-liquid behavior., Comment: 5 pages, 3 figures, Eq. 1 typo corrected from previous version

We study the ternary clathrate ${\mathrm{Pr}}_{3}{\mathrm{Pd}}_{20}{\mathrm{Si}}_{6}$ in specific heat and ac susceptibility measurements on a high-quality single crystal, distinguishing antiferromagnetic and antiferroquadrupolar ordering, as well as a hitherto unknown magnetic low-temperature transition. The specific heat shows the direct involvement of nuclear spin degrees of freedom in the antiferromagnetic ordering, which is well supported by our calculation of the hyperfine level scheme without adjustable parameters. ${\mathrm{Pr}}_{3}{\mathrm{Pd}}_{20}{\mathrm{Si}}_{6}$ is, therefore, one of the rare materials where the nuclear moments are involved in the formation of the magnetic ground state.

We study the ternary clathrate Pr3Pd20Si6 in specific heat and ac susceptibility measurements on a high-quality single crystal, distinguishing antiferromagnetic and antiferroquadrupolar ordering, as well as a hitherto unknown magnetic low-temperature transition. The specific heat shows the direct involvement of nuclear spin degrees of freedom in the antiferromagnetic ordering, which is well supported by our calculation of the hyperfine level scheme without adjustable parameters. Pr3Pd20Si6 is, therefore, one of the rare materials where the nuclear moments are involved in the formation of the magnetic ground state.

A current of electrons traversing a landscape of localized spins possessing non-coplanar magnetic order gains a geometrical (Berry) phase which can lead to a Hall voltage independent of the spin-orbit coupling within the material--a geometrical Hall effect. We show that the highly-correlated metal UCu5 possesses an unusually large controllable geometrical Hall effect at T, article and supplemental information

In this chapter we give an overview on some recent experimental results on vortex dynamics in the non-centrosymmetric superconductors \(\hbox{CePt}_3\hbox{Si}\) and \(\hbox{Li}_2\hbox{Pt}_3\hbox{B}\). In both compounds the flux creep from a metastable vortex configuration is anomalously slow—slower than in any other superconductor. Additionally, \(\hbox{Li}_2\hbox{Pt}_3\hbox{B}\) shows very strong avalanche-like flux release after waiting times of several hours at millikelvin temperatures. Since critical currents are also low, the origin of these properties cannot be simply attributed to conventional flux pinning by defects. We speculate that both properties might be connected with crystalline twinning of the samples. We show that twin boundaries in non-centrosymmetric superconductors can host states with broken time reversal symmetry which can carry fractionally quantized flux lines. These flux lines are strongly pinned to the twin boundaries such that they impede the usual flux motion without affecting the critical current.

In this paper we investigate the quantum phase transition from magnetic Bose glass to magnetic Bose-Einstein condensation induced by a magnetic field in NiCl2.4SC(NH2)2 (dichloro-tetrakis-thiourea-Nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z=d; moreover the correlation length exponent is found to be nu = 0.75(10) and the order parameter exponent to be beta = 0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher et al., [Phys. Rev. B 40, 546 (1989)], but they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator., Comment: 12 pages, 10 figures

In order to examine the nature of the superconducting order parameter in UBe13, we measured the specific heat, C, as a function of temperature, T, under uniaxial stress along 〈1 0 0〉 axis, for both “L”- (T c ≈0.75 K ) and “H”-type (0.85⩽T c ⩽0.95 K ) crystals. With increasing pressure, a linear decrease of the superconducting transition temperature, Tc, was observed ( ∂ T c / ∂ p≃8.5 mK/GPa for “L”-type and ∂ T c / ∂ p≃50 mK/GPa for “H”-type) but no split of the transition could be resolved unambiguously for either of the two samples within our measurement resolution.

We investigated the superconducting gap structure of SrNi${}_{2}$P${}_{2}$ (${T}_{\mathrm{c}}=1.4$ K) via low-temperature magnetothermal conductivity $\ensuremath{\kappa}(T,H)$ measurements. Zero field thermal conductivity $\ensuremath{\kappa}$ decreases exponentially $\ensuremath{\kappa}\ensuremath{\propto}$ exp($\ensuremath{-}{\mathit{aT}}_{\mathrm{c}}/T$) with $a=$ 1.5, in accord with the BCS theory, and rolls over to a phonon-like $\ensuremath{\kappa}\ensuremath{\propto}{T}^{3}$ behavior at low temperature, similar to a number of conventional $s$-wave superconductors. In addition, we observed a ``concave'' field dependence of the residual linear term ${\ensuremath{\kappa}}_{0}(H)/T$. These facts strongly rule out the presence of nodes in the superconducting energy gap of SrNi${}_{2}$P${}_{2}$. Together with a fully gapped Fermi surface in the superconducting state of BaNi${}_{2}$As${}_{2}$ (${T}_{\mathrm{c}}=$ 0.6--0.7 K), demonstrated in our recent work, these results lead us to stipulate that fully gapped superconductivity is likely to be a universal feature of Ni-based pnictide superconductors.

We have performed low-temperature specific heat $C$ and thermal conductivity $\kappa$ measurements on the Ni-pnictide superconductors BaNi$_2$As$_2$ ($T_\mathrm{c}$=0.7 K and SrNi$_2$P$_2$ ($T_\mathrm{c}$=1.4 K). The temperature dependences $C(T)$ and $\kappa(T)$ of the two compounds are similar to the results of a number of s-wave superconductors. Furthermore, the concave field responses of the residual $\kappa$ for BaNi$_2$As$_2$ rules out the presence of nodes on the Fermi surfaces. We postulate that fully gapped superconductivity could be universal for Ni-pnictide superconductors. Specific heat data on Ba$_{0.6}$La$_{0.4}$Ni$_2$As$_2$ shows a mild suppression of $T_\mathrm{c}$ and $H_\mathrm{c2}$ relative to BaNi$_2$As$_2$., Comment: 5 pages, 3 figures, to be published in J. Phys.: Conf. Ser

We report specific heat $(C)$ and magnetization $(M)$ of single crystalline ${\text{Ce}}_{4}{\text{Pt}}_{12}{\text{Sn}}_{25}$ at temperature down to $\ensuremath{\sim}50\text{ }\text{mK}$ and in fields up to 3 T. $C/T$ exhibits a sharp anomaly at 180 mK, with a large $\ensuremath{\Delta}C/T\ensuremath{\sim}30\text{ }\text{J}/\text{mol}\text{ }\text{Ce}\text{ }{\text{K}}^{2}$, which, together with the corresponding cusplike magnetization anomaly, indicates an antiferromagnetic (AFM) ground state with a N\'eel temperature ${T}_{\text{N}}=180\text{ }\text{m}\text{ }\text{K}$. Numerical calculations based on a Heisenberg model reproduce both zero-field $C$ and $M$ data, thus placing ${\text{Ce}}_{4}{\text{Pt}}_{12}{\text{Sn}}_{25}$ in the weak exchange coupling $Jl{J}_{\text{c}}$ limit of the Doniach diagram, with a very small Kondo scale ${T}_{\text{K}}⪡{T}_{\text{N}}$. Magnetic field suppresses the AFM state at ${H}^{\ensuremath{\ast}}\ensuremath{\approx}0.7\text{ }\text{T}$, much more effectively than expected from the Heisenberg model, indicating additional effects possibly due to frustration or residual Kondo screening.

We report on the vortex dynamics of a single crystal of the non-centrosymmetric heavy-fermion superconductor CePt$_{3}$Si. Decays of the remnant magnetization display a clean logarithmic time dependence with rates that follow the temperature dependence expected from the Kim-Anderson theory. The creep rates are lower than observed in any other centrosymmetric superconductor and are not caused by high critical currents. On the contrary, the critical current in CePt$_{3}$Si is considerably lower than in other superconductors with strong vortex pinning indicating that an alternative impediment on the flux line motion might be at work in this superconductor., Comment: 4 pages, 5 figures

We investigated the vortex dynamics in the non-centrosymmetric superconductor Li_2Pt_3B in the temperature range 0.1 K - 2.8 K. Two different logarithmic creep regimes in the decay of the remanent magnetization from the Bean critical state have been observed. In the first regime, the creep rate is extraordinarily small, indicating the existence of a new, very effective pinning mechanism. At a certain time a vortex avalanche occurs that increases the logarithmic creep rate by a factor of about 5 to 10 depending on the temperature. This may indicate that certain barriers against flux motion are present and they can be opened under increased pressure exerted by the vortices. A possible mechanism based on the barrier effect of twin boundaries is briefly discussed.

We report low-temperature thermal conductivity down to 40 mK of the antiferromagnet ${\text{BaFe}}_{2}{\text{As}}_{2}$, which is the parent compound of recently discovered iron-based superconductors. In the investigated temperature range below 4 K, the thermal conductivity $\ensuremath{\kappa}$ is well described by the expression $\ensuremath{\kappa}=aT+b{T}^{2.22}$. We attribute the ``$aT$''-term to an electronic contribution which is found to satisfy the Wiedemann-Franz law in the $T\ensuremath{\rightarrow}0\text{ }\text{K}$ limit and the remaining thermal conductivity, $\ensuremath{\sim}{T}^{2.22}$, is attributed to phonon conductivity. A small influence on thermal conductivity by magnetic fields up to 8 T is well accounted by the observed magnetoresistance. The result is consistent with a fully gapped magnon spectrum, inferred previously from inelastic neutron scattering measurements.

We studied the temperature-pressure phase diagram of ${\text{EuFe}}_{2}{\text{As}}_{2}$ by electrical resistivity measurements. The spin-density-wave transition at ${T}_{0}$ associated with the FeAs-layers is continuously suppressed with increasing pressure, while the antiferromagnetic ordering temperature of the ${\text{Eu}}^{2+}$ moments seems to be nearly pressure independent up to 2.6 GPa. Above 2 GPa a sharp drop of the resistivity, $\ensuremath{\rho}(T)$, indicates the onset of superconductivity at ${T}_{c}\ensuremath{\approx}29.5\text{ }\text{K}$. Surprisingly, on further reducing the temperature, $\ensuremath{\rho}(T)$ is increasing again and exhibiting a maximum caused by the ordering of the ${\text{Eu}}^{2+}$ moments, a behavior which is reminiscent of reentrant superconductivity as it is observed in the ternary Chevrel phases or in the rare-earth nickel borocarbides.

We present experimental results of low-temperature x-ray synchrotron diffraction, neutron-scattering, and very low-temperature (mK range) bulk measurements on the nanotube system Na2 V3 O7. The crystal structure determined from our data is similar to the previously proposed model, but also deviates from it in significant details. The structure comprises of nanotubes along the c axis formed by stacking units of two V rings buckled in the ab plane. The space group is P 3 and the composition is nonstoichiometric, Na2-x V3 O7, x=0.17. The thermal evolution of the lattice parameters reveals anisotropic lattice compression on cooling. Neutron-scattering experiments monitor a very weak magnetic signal at energies from -20 to 9 meV. Magnetic susceptibility, specific-heat measurements, and decay of remanent magnetization in the 30-300 mK range reveal that the previously observed transition at ≈76 mK is spin-glass like with no long-range order. Presented experimental observations do not support models of isolated clusters but are compatible with a model of odd-legged S=1/2 spin tubes possibly segmented into fragments with different lengths. © 2008 The American Physical Society.

CeCoIn5 exhibits the highest superconducting transition temperature (Tc = 2.3 K) among the Ce‐based heavy‐fermion compounds. Power‐law dependencies in specific heat (C), thermal conductivity (κ), and nuclear spin‐lattice relaxation rate (1/T1) for T ≪ Tc point to an unconventional superconducting state. Within the superconducting state specific‐heat shows an anomaly in the vicinity of the upper critical field Hc2 = 11.6 T for magnetic field parallel to the c‐axis. This phase‐transition is discussed as possible realization of a Fulde‐Ferrell‐Larkin‐Ovchinnikov (FFLO) phase. On the other hand, CeCoIn5 is located close to an antiferromagnetic (AFM) quantum critical point (QCP) at ambient pressure and underlying magnetic fluctuations may be responsible for the specific‐heat feature. We present first results of a specific‐heat study under pressure and in high magnetic fields to clarify the origin of this phase.

In this paper, we report on the structural, optical, and electrical properties of a wide compositional range of AlxIn1−xN thin layers deposited on glass and polyethylene terephthalate substrates. AlxIn1−xN layers of controlled composition were obtained by a simple reactive magnetron co-sputtering protocol, using a single aluminium target with indium insets, by varying the Al/In target surface area ratio, and the composition of the deposition atmosphere. The relevant physical properties were investigated and discussed. It is shown that the texture of the thin films is dependent on the cation ratio, while the bowing parameters of lattice constants and band gap values are larger than those of epitaxial layers.

The heavy-fermion superconductor (SC) CeCoIn 5 shows an anomaly in specific heat, inside the SC state, at low temperatures and close to the upper critical field ( B c 2 ) . This feature was attributed to a phase transition from the classical vortex state into a Fulde–Ferrell–Larkin–Ovchinnikov phase. Intriguingly, at ambient pressure, CeCoIn 5 is situated close to an antiferromagnetic quantum critical point (QCP) and underlying magnetic fluctuations may be responsible for the specific heat feature. By applying pressure, the system is driven away from the QCP. We present first results of a specific heat study under hydrostatic pressure and in high magnetic fields as an attempt to clarify the origin of this phase.

The effect of dilute La substitution in Ce 1- x La x RhIn 5 (0 ≤ x ≤0.07) has been investigated macroscopically by specific heat measurement and microscopically by nuclear magnetic/quadrupole resonance (NMR/NQR). The Neel temperature decreases gradually by dilute La substitutions from 3.8 K ( x =0) to 2.9 K ( x =0.07). The specific heat for Ce 1- x La x RhIn 5 exhibits nuclear Schottky contributions below 1 K, which are compatible with the microscopic parameters obtained by NMR/NQR. Below the Neel temperature, the residual Sommerfeld coefficient of ∼50 mJ K -2 /mol is nearly independent of increasing La substitution, while the entropy in the ordered state is slightly enhanced. Microscopically, 1/ T 1 in the AF ordered state can be explained by spin-wave term of 4 f moments, spin fluctuation term by uncompensated localized Ce moments near the La ions, and a small Korringa contribution by non-4 f electrons, which suggests a localized 4 f nature in CeRhIn 5 .

We report specific heat (C) and magnetization (M) of single crystalline Ce4Pt12Sn25 at temperature down to ≈ 50 mK and in fields up to 3 T. C/T exhibits a sharp anomaly at 180 mK, with a large jump in a Sommerfeld coefficient γ = C/T of Δγ = 30 J/molK2-Ce, which, together with corresponding cusp-like magnetization anomaly, indicate antiferromagnetic (AFM) ground state with Nel temperature TN = 0.18 K. Numerical calculations based on Heisenberg model reproduce well zero field specific heat data, and point to a very small Kondo scale TK, clearly placing Ce4Pt12Sn25 in the weak exchange coupling J < Jc limit of the Doniac diagram. Magnetic field suppresses AFM state at H* ≈ 0.7 T, much more rapidly than indicated by theoretical calculations.

We report on low-temperature thermal conductivity of the noncentrosymmetric superconductor LaRhSi3 (TC = 2.3K), which is a paramagnetic analog of the pressure-induced superconductor CeRhSi3. In the normal state (either in zero field above Tc, or in magnetic field above Hc2), the thermal conductivity k is mostly due to electrons, and shows a nearly T-linear dependence. In the superconducting state, k decreases exponentially below Tc, and crosses over to κ ∝ T2 behavior at T << Tc. The temperature dependence of thermal conductivity of LaRhSi3 is similar to that of a number of conventional s-wave superconductors. The field dependence of the residual linear term κ0/T as a function of magnetic field suggests that LaRhSi3 has no nodes in the superconducting gap.

We report here the results of high pressure conductivity measurements on TlxV6S8 (x = 1, 0.15, 0.47, and 0.63) in pressure range from 0 - 2 GPa in the temperature range from 300 K to 300 mK to obtain insight in the competition between superconductivity and charge density waves as well as to establish the existence of a charge density wave in these materials. The experimental results are complemented by first principle electronic band structure calculations on InV6S8 in order to study the effect of pressure on the Fermi surface nesting which leads to the formation of the charge density wave instability.