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Register a new userNon-metallic, non-Fermi-liquid resistivity of FeCrAs from 0 to 17 GPa
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An unusual, non-metallic resistivity of the 111 iron-pnictide compound FeCrAs is shown to be relatively unchanged under pressures of up to 17 GPa. Combined with our previous finding that this non-metallic behaviour persists from at least 80 mK to 800 K, this shows that the non-metallic phase is exceptionally robust. Antiferromagnetic order, with a Neel temperature T_N ~ 125 K at ambient pressure, is suppressed at a rate of 7.1 +/- 0.1 K/GPa, falling to below 50 K at 10 GPa. We conclude that formation of a spin-density wave gap at T_N does not play an important role in the non-metallic resistivity of FeCrAs at low temperatures.
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Non-Fermi liquid behaviour in single-crystalline U2Pt2In has been studied by means of resistivity experiments (I||c) under hydrostatic pressure (P<1.5 GPa). At ambient pressure the resistivity rho(T) follows a power law rho~T^alpha with alpha~0.5. Upon applying pressure alpha increases. For P>1 GPa a minimum develops in rho(T). A study of the field dependence of the minimum confirms its magnetic origin. The ratio c/a is proposed as the effective control parameter, rather than the unit cell volume.
We report transport and thermodynamic properties of stoichiometric single crystals of the hexagonal iron-pnictide FeCrAs. The in-plane resistivity shows an unusual non-metallic dependence on temperature T, rising continuously with decreasing T from ~ 800 K to below 100 mK. The c-axis resistivity is similar, except for a sharp drop upon entry into an antiferromagnetic state at T_N 125 K. Below 10 K the resistivity follows a non-Fermi-liquid power law, rho(T) = rho_0 - AT^x with x<1, while the specific heat shows Fermi liquid behaviour with a large Sommerfeld coefficient, gamma ~ 30 mJ/mol K^2. The high temperature properties are reminiscent of those of the parent compounds of the new layered iron-pnictide superconductors, however the T -> 0 properties suggest a new class of non-Fermi liquid.
We have investigated hexagonal YbAgGe down to 70 mK by measuring the magnetic-field and temperature dependence of the resistivity rho of single crystals in fields up to 14 T. Our results extend the H-T phase diagram to the lowest temperatures for H applied in the basal plane and along the c-axis. In particular, critical fields for the suppression of several magnetic phases are determined. The temperature dependence of rho(T) is unusual: whereas at low H, rho(T) reveals a temperature exponent n>=2, we find 1<=n<1.5 and strong enhancement of the temperature dependence of rho(T) close to and beyond the highest critical field for each field direction. For H applied in the basal plane, at high fields a conventional T^2 dependence of rho(T) is reached above 10 T accompanied by an approach to saturation of a strong drop in the residual resistivity. YbAgGe appears to be one of few Yb-based stoichiometric systems, where quantum-critical behaviour may be induced by a magnetic field.
FeCrAs displays an unusual electrical response that is neither metallic in character nor divergent at low temperatures, as expected for an insulating response, and therefore it has been termed a nonmetal-metal. We carried out neutron scattering experiments on powder and single crystal samples to study the magnetic dynamics and critical fluctuations in FeCrAs. Magnetic neutron diffraction measurements find Cr3+ magnetic order setting in at 115 K with the mean-field critical exponent. Neutron spectroscopy, however, observes gapless stiff magnetic fluctuations emanating from magnetic positions with propagation wave vector q_0=(1/3,1/3), which persists up to at least 80 meV. The magnetism in FeCrAs therefore displays a response which resembles that of itinerant magnets at high energy transfers, such as chromium alloys. We suggest that the presence of stiff high-energy spin fluctuations is the origin of the unusual temperature dependence of the resistivity.
We report transport and thermodynamic properties of single-crystal SrIrO3 as a function of temperature T and applied magnetic field H. We find that SrIrO3 is a non-Fermi-liquid metal near a ferromagnetic instability, as characterized by the following properties: (1) small ordered moment but no evidence for long-range order down to 1.7 K; (2) strongly enhanced magnetic susceptibility that diverges as T or T1/2 at low temperatures, depending on the applied field; (3) heat capacity C(T,H) ~ -Tlog T that is readily amplified by low applied fields; (4) a strikingly large Wilson ratio at T< 4K; and (5) a T3/2-dependence of electrical resistivity over the range 1.7 < T < 120 K. A phase diagram based on the data implies SrIrO3 is a rare example of a stoichiometric oxide compound that exhibits non-Fermi-liquid behavior near a quantum critical point (T = 0 and H = 0.23 T).
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