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M. F. Hundley

Publications and source records attributed to M. F. Hundley.

At least 19 recordsLinked to original sources
arXiv2010

Unusual metamagnetism in CeIrIn$_5$

We report a high field investigation (up to 45 T) of the metamagnetic transition in CeIrIn$_5$ with resistivity and de-Haas-van-Alphen (dHvA) effect measurements in the temperature range 0.03-1 K. As the magnetic field is increased the resistivity increases, reaches a maximum at the metamagnetic critical field, and falls precipitously for fields just above the transition, while the amplitude of all measurable dHvA frequencies are significantly attenuated near the metamagnetic critical field. However, the dHvA frequencies and cyclotron masses are not substantially altered by the transition. In the low field state, the resistivity is observed to increase toward low temperatures in a singular fashion, a behavior that is rapidly suppressed above the transition. Instead, in the high field state, the resistivity monotonically increases with temperature with a dependence that is more singular than the iconic Fermi-liquid, temperature-squared, behavior. Both the damping of the dHvA amplitudes and the increased resistivity near the metamagnetic critical field indicate an increased scattering rate for charge carriers consistent with critical fluctuation scattering in proximity to a phase transition. The dHvA amplitudes do not uniformly recover above the critical field, with some hole-like orbits being entirely suppressed at high fields. These changes, taken as a whole, suggest that the metamagnetic transition in CeIrIn$_5$ is associated with the polarization and localization of the heaviest of quasiparticles on the hole-like Fermi surface.

cond-mat.str-el↗
arXiv2008

Giant Magnetoelectric Effect in a Multiferroic Material with a High Ferroelectric Transition Temperature

We present a unique example of giant magnetoelectric effect in a conventional multiferroic HoMnO3, where polarization is very large (~56 mC/m2) and the ferroelectric transition temperature is higher than the magnetic ordering temperature by an order. We attribute the uniqueness of the giant magnetoelectric effect to the ferroelectricity induced entirely by the off-center displacement of rare earth ions with large magnetic moments. This finding suggests a new avenue to design multiferroics with large polarization and higher ferroelectric transition temperature as well as large magnetoelectric effects.

cond-mat.str-el↗
arXiv2007

Heat Capacity in Magnetic and Electric Fields Near the Ferroelectric Transition in Tri-Glycine Sulfate

Specific-heat measurements are reported near the Curie temperature ($T_C$~= 320 K) on tri-glycine sulfate. Measurements were made on crystals whose surfaces were either non-grounded or short-circuited, and were carried out in magnetic fields up to 9 T and electric fields up to 220 V/cm. In non-grounded crystals we find that the shape of the specific-heat anomaly near $T_C$ is thermally broadened. However, the anomaly changes to the characteristic sharp $λ$-shape expected for a continuous transition with the application of either a magnetic field or an electric field. In crystals whose surfaces were short-circuited with gold, the characteristic $λ$-shape appeared in the absence of an external field. This effect enabled a determination of the critical exponents above and below $T_C$, and may be understood on the basis that the surface charge originating from the pyroelectric coefficient, $dP/dT$, behaves as if shorted by external magnetic or electric fields.

cond-mat.stat-mech↗
arXiv2006

Effect of Delocalized Vortex Core States on the Specific Heat of Nb

The magnetic field (B) dependence of the electronic specific heat for a simple BCS type-II superconductor has been determined from measurements on pure niobium (Nb). Contrary to expectations, the electronic specific heat coefficient gamma(T,B) is observed to be a sublinear function of B at fields above the lower critical field H_{c1}. This behavior is attributed to the delocalization of quasiparticles bound to the vortex cores. The results underscore the ambiguity of interpretation that arises in specific heat studies of this kind on newly discovered type-II superconductors, and also emphasize the need to such measurements under field-cooled conditions.

cond-mat.supr-con↗
arXiv2005

c-axis magnetotransport in CeCoIn$_{5}$

We present the results of out-of-plane electrical transport measurements on the heavy fermion superconductor CeCoIn$_{5}$ at temperatures from 40 mK to 400 K and in magnetic field up to 9 T. For $T <$ 10 K transport measurements show that the zero-field resistivity $ρ_{c}$ changes linearly with temperature and extrapolates nearly to zero at 0 K, indicative of non-Fermi-liquid (nFL) behavior associated with a quantum critical point (QCP). The longitudinal magnetoresistance (LMR) of CeCoIn$_{5}$ for fields applied parallel to the c-axis is negative and scales as $B/(T+T^{*})$ between 50 and 100 K, revealing the presence of a single-impurity Kondo energy scale $T^{*} \sim 2$ K. Beginning at 16 K a small positive LMR feature is evident for fields less than 3 tesla that grows in magnitude with decreasing temperature. For higher fields the LMR is negative and increases in magnitude with decreasing temperature. This sizable negative magnetoresistance scales as $B{^2}/T$ from 2.6 K to roughly 8 K, and it arises from an extrapolated residual resistivity that becomes negative and grows quadratically with field in the nFL temperature regime. Applying a magnetic field along the c-axis with B $>$ B$_{c2}$ restores Fermi-liquid behavior in $ρ_{c}(T)$ at $T$ less than 130 mK. Analysis of the $T{^2}$ resistivity coefficient's field-dependence suggests that the QCP in CeCoIn$_{5}$ is located \emph{below} the upper critical field, inside the superconducting phase. These data indicate that while high-$T$ c-axis transport of CeCoIn$_{5}$ exhibits features typical for a heavy fermion system, low-$T$ transport is governed both by spin fluctuations associated with the QCP and Kondo interactions that are influenced by the underlying complex electronic structure intrinsic to the anisotropic CeCoIn$_{5}$ crystal structure.

cond-mat.str-el↗
arXiv2005

Anomalous Paramagnetic Effects in the Mixed State of LuNi2B2C

Anomalous paramagnetic effects in dc magnetization were observed in the mixed state of LuNi2B2C, unlike any reported previously. It appears as a kink-like feature for H > 30 kOe and becomes more prominent with increasing field. A specific heat jump at the corresponding temperature suggests that the anomaly is due to a true bulk transition. A magnetic flux transition from a square to an hexagonal lattice is consistent with the anomaly.

cond-mat.supr-con↗
arXiv2004

Antiferromagnetism in Pr3In: Singlet/triplet physics with frustration

We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu3Au structure) compound Pr3In. This compound is believed to have a singlet (Gamma1) groundstate and a low-lying triplet (Gamma4) excited state. In addition, nearest-neighbor antiferromagnetic interactions are frustrated in this structure. Antiferromagnetic order occurs below T_N = 12K with propagation vector (0, 0, 0.5 +/-δ) where δ\approx 1/12. The neutron diffraction results can be approximated with the following model: ferromagnetic sheets from each of the three Pr sites alternate in sign along the propagation direction with a twelve-unit-cell square-wave modulation. The three moments of the unit cell of 1 μ_B magnitude are aligned so as to sum to zero as expected for nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12K, there is a transition near 70K below which there is a small (0.005 μ_B) ferromagnetic moment. There is considerable field and sample dependence to these transitions. The specific heat data show almost no anomaly at TN = 12K. This may be a consequence of the induced moment in the Gamma1 singlet, but may also be a sample-dependent effect.

cond-mat.str-el↗
arXiv2004

Field-Tuned Quantum Critical Point in CeCoIn$_5$ Near the Superconducting Upper Critical Field

We report a systematic study of high magnetic field specific heat and resistivity in single crystals of CeCoIn_5 for the field oriented in the basal plane (H//ab) of this tetragonal heavy fermion superconductor. We observe a divergent electronic specific heat as well as an enhanced A coefficient of the T^{2} law in resistivity at the lowest temperatures, as the field approaches the upper critical field of the superconducting transition. Together with the results for field along the tetragonal axis (H//c), the emergent picture is that of a magnetic field tuned quantum critical point which exists in the vicinity of the superconducting H_{c2} despite a variation of a factor of 2.4 in H_{c2} for different field orientations. This suggests an underlying physical reason exists for the superconducting H_{c2} to coincide with the quantum critical field. Moreover, we show that the recovery of a Fermi Liquid ground state with increasing magnetic field is more gradual, meaning that the fluctuations responsible for the observed quantum critical phenomena are more robust with respect to magnetic field, when the magnetic field is applied in-plane. Together with the close proximity of the quantum critical point and H_{c2} in CeCoIn_5 for both field orientation, the anisotropy in the recovery of the Fermi liquid state might constitute an important piece of information in identifying the nature of the fluctuations that become critical.

cond-mat.str-el↗
arXiv2004

High pressure investigation of the heavy-fermion antiferromagnet U_3Ni_5Al_19

Measurements of magnetic susceptibility, specific heat, and electrical resistivity at applied pressures up to 55 kbar have been carried out on single crystals of the heavy-fermion antiferromagnet U_3Ni_5Al_19, which crystallizes in the Gd_3Ni_5Al_19 orthorhombic structure with two inequivalent U sites. At ambient pressure, a logarithmic T-dependence of the specific heat and T-linear electrical resistivity below 5 K indicates non-Fermi liquid (NFL) behavior in the presence of bulk antiferromagnetic order at T_N=23 K. Electrical resistivity measurements reveal a crossover from non-Fermi liquid to Fermi liquid behavior at intermediate pressures between 46 kbar and 51 kbar, followed by a return to NFL T^{3/2} behavior at higher pressures. These results provide evidence for an ambient pressure quantum critical point and an additional antiferromagnetic instability at P_c=60 kbar.

cond-mat.str-el↗
arXiv2004

A Novel Dielectric Anomaly in Cuprates and Nickelates: Signature of an Electronic Glassy State

The low-frequency dielectric response of hole-doped insulators La_{2}Cu_{1-x}Li_{x}O_{4} and La_{2-x}Sr_{x}NiO_{4} shows a large dielectric constant ε^{'} at high temperature and a step-like drop by a factor of 100 at a material-dependent low temperature T_{f}. T_{f} increases with frequency and the dielectric response shows universal scaling in a Cole-Cole plot, suggesting that a charge glass state is realized both in the cuprates and in the nickelates.

cond-mat.str-el↗
arXiv2004

Anomalous f-electron Hall Effect in the Heavy-Fermion System CeTIn$_{5}$ (T = Co, Ir, or Rh)

The in-plane Hall coefficient $R_{H}(T)$ of CeRhIn$_{5}$, CeIrIn$_{5}$, and CeCoIn$_{5}$ and their respective non-magnetic lanthanum analogs are reported in fields to 90 kOe and at temperatures from 2 K to 325 K. $R_{H}(T)$ is negative, field-independent, and dominated by skew-scattering above $\sim$ 50 K in the Ce compounds. $R_{H}(H \to 0)$ becomes increasingly negative below 50 K and varies with temperature in a manner that is inconsistent with skew scattering. Field-dependent measurements show that the low-T anomaly is strongly suppressed when the applied field is increased to 90 kOe. Measurements on LaRhIn$_{5}$, LaIrIn$_{5}$, and LaCoIn$_{5}$ indicate that the same anomalous temperature dependence is present in the Hall coefficient of these non-magnetic analogs, albeit with a reduced amplitude and no field dependence. Hall angle ($θ_{H}$) measurements find that the ratio $ρ_{xx}/ρ_{xy}=\cot(θ_{H})$ varies as $T^{2}$ below 20 K for all three Ce-115 compounds. The Hall angle of the La-115 compounds follow this T-dependence as well. These data suggest that the electronic-structure contribution dominates the Hall effect in the 115 compounds, with $f$-electron and Kondo interactions acting to magnify the influence of the underlying complex band structure. This is in stark contrast to the situation in most $4f$ and $5f$ heavy-fermion compounds where the normal carrier contribution to the Hall effect provides only a small, T-independent background to $R_{H}.$

cond-mat.str-el↗
arXiv2004

Anisotropy of Thermal Conductivity and Possible Signature of the Fulde-Ferrell-Larkin-Ovchinnikov state in CeCoIn_5

We have measured the thermal conductivity of the heavy-fermion superconductor CeCoIn_5 in the vicinity of the upper critical field, with the magnetic field perpendicular to the c axis. Thermal conductivity displays a discontinuous jump at the superconducting phase boundary below critical temperature T_0 ~ 1 K, indicating a change from a second to first order transition and confirming the recent results of specific heat measurements on CeCoIn_5. In addition, the thermal conductivity data as a function of field display a kink at a field H_k below the superconducting critical field, which closely coincides with the recently discovered anomaly in specific heat, tentatively identified with the appearance of the spatially inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state. Our results indicate that the thermal conductivity is enhanced within the FFLO state, and call for further theoretical investigations of the order parameter's real space structure (and, in particular, the structure of vortices) and of the thermal transport within the inhomogeneous FFLO state.

cond-mat.str-el↗
arXiv2002

Magnetic Properties of Heavy Fermion Superconductors CeRhIn5 and Ce2RhIn8

Some recent neutron scattering works on CeRhIn5 and Ce2RhIn8, together with related resistivity and specific heat measurements, are summarized. In spite of its layered crystal structure, CeRhIn5 is shown to be 3-dimensional both magnetically and in transport. We also find that the Fisher-Langer behavior is closely followed in CeRhIn5. This may circumvent the Kondo lattice model and support applying established Fermi-liquid superconductivity theory to heavy fermion superconductors.

cond-mat.str-el↗
arXiv2002

Low Temperature Thermal Transport in High Temperature Superconducting BSCCO via Y-doped Insulating Analogue

In order to separate electronic and phonon mechanisms of thermal transport in high temperature superconducting Bi2212, we measured thermal conductivity of single crystals of Y-doped Bi2212, an insulating analogue of pure Bi2212, in the temperature range between 40 mK and 2 K. Temperature dependence of the thermal conductivity of insulating samples changes from T$^{1.7}$ between 1 and 2 K to $T^{2.6}$ below 200 mK, indicating saturation of the phonon mean free path with decreasing temperature. Overall, thermal conductivity of the insulating samples (which is due entirely to phonons) is strongly suppressed in comparison to that of the superconducting samples. Therefore, a large (and at the lowest temperatures, predominant) part of the total thermal transport in superconducting Bi2212 is due to electrons.

cond-mat.supr-con↗
arXiv2001

Evidence for LineLike Vortex Liquid Phase in Tl$_2$Ba$_2$CaCu$_2$O$_8$ Probed by the Josephson Plasma Resonance

We measured the Josephson plasma resonance (JPR) in optimally doped Tl$_2$Ba$_2$CaCu$_2$O$_{8+δ}$ thin films using terahertz time-domain spectroscopy in transmission. The temperature and magnetic field dependence of the JPR frequency shows that the c-axis correlations of pancake vortices remain intact at the transition from the vortex solid to the liquid phase. In this respect Tl$_2$Ba$_2$CaCu$_2$O$_{8+δ}$ films, withanisotropy parameter $γ\approx 150$, are similar to the less anisotropic YBa$_2$Cu$_3$O$_{7-δ}$ $(γ\approx 8)$ rather than to the most anisotropic Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ single crystals $γ\geq 500$).

cond-mat.supr-con↗
arXiv2001

Specific Heat of CeRhIn5: Pressure-Driven Evolution of the Ground State from Antiferromagnetism to Superconductivity

Measurements of the specific heat of antiferromagnetic CeRhIn5, to 21 kbar, and for 21 kbar to 70 kOe, show a discontinuous change from an antiferromagnetic ground state below 15 kbar to a superconducting ground state above, and suggest that it is accompanied by a weak thermodynamic first-order transition. Bulk superconductivity appears, apparently with d-wave electron pairing, at the critical pressure, 15 kbar; with further increase in pressure a residual temperature-proportional term in the specific heat disappears.

cond-mat.str-el↗
arXiv2001

Unusual kondo behavior in the indium-rich heavy fermion antiferromagnet Ce3Pt4In13

We report the thermodynamic, magnetic, and electronic transport properties of the new ternary intermetallic system (Ce,La)3Pt4In13. Ce3Pt4In13 orders antiferromagnetically at 0.95 K while the non-magnetic compound La3Pt4In13 is a conventional 3.3 K superconductor. Kondo lattice effects appear to limit the entropy associated with the Neel transition to (1/4)Rln2 as an electronic contribution to the specific heat of gamma = 1 J/mole-Ce K2 is observed at TN; roughly 35% of this gamma survives the ordering transition. Hall effect, thermoelectric power, and ambient-pressure resistivity measurements confirm this interpretation. These results suggest that RKKY and Kondo interactions are closely balanced in this compound (TN = TK). Contrary to expectations based on the Doniach Kondo necklace model, applied hydrostatic pressure modestly enhances the magnetic ordering temperature with dTN/dP = +23 mK/kbar. As such Ce3Pt4In13 provides a counterexample to Kondo systems with similar Kondo and RKKY energy scales wherein applied pressure enhances TK at the expense of the ordered magnetic state.

cond-mat.str-el↗