Antiferromagnetic critical pressure in URu2Si2 under hydrostatic conditions

The onset of antiferromagnetic order in URu2Si2 has been studied via neutron diffraction in a helium pressure medium, which most closely approximates hydrostatic conditions. The antiferromagnetic critical pressure is 0.80 GPa, considerably higher than values previously reported. Complementary electrical resistivity measurements imply that the hidden order-antiferromagnetic bicritical point far exceeds 1.02 GPa. Moreover, the redefined pressure-temperature phase diagram suggests that the superconducting and antiferromagnetic phase boundaries actually meet at a common critical pressure at zero temperature.Comment: 5 pgs, 4 figs; AFM ordered moment revised to 0.5 muB, added and corrected citations and reference

Boundary scattering in micro-size crystal of topological Kondo insulator SmB6_6

We have studied the effects of phonon-boundary scattering on the thermal transport in topological Kondo insulator, SmB$_6$. The studies have been performed by using the $3\omega$ method in the temperature range 300K - 3K. We show that the observed thermal conductivity of micro-size SmB$_6$ is of the order of magnitude smaller than for a bulk single-crystal. Using the Callaway model we analyzed the low-temperature lattice thermal conductivity of the micro crystal and show that phonon scattering by sample boundaries plays a major role in the thermal resistance in this topological material. In addition, we show that the temperature dependence of the lattice thermal conductivity shows a double peak structure that suggests complex phonon-phonon or phonon-defects interactions in SmB$_6$. These findings provide guidance for the understanding of the thermal transport of advanced materials and devices at a micro-scale.Comment: 5 pages including references, 3 figure

Pressure-resistant intermediate valence in Kondo insulator SmB6

Resonant x-ray emission spectroscopy (RXES) was used to determine the pressure dependence of the f-electron occupancy in the Kondo insulator SmB6. Applied pressure reduces the f-occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. Over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure

Annual Scientific Progress Report: National Nuclear Security Administration Stewardship Stockpile: Academic Alliance Research Grant #DE-FG52-06NA26205

The focus of this grant, entitled ''Experimental investigations of magnetic, superconducting, and other phase transitions in novel f-electron materials at ultra-high pressures using designer diamond anvils'', is to explore the novel properties of f-electron compounds under pressure, with a particular emphasis on the physics of superconductivity, magnetism, and their interactions. This report is a synopsis of the research that was undertaken from 6/2006-6/2007

Tuning of Hidden Order and Superconductivity in URu2Si2 by Applied Pressure and Re Substitution

Single crystals of URu2-xRexSi2 have been grown via the Czochralski technique. Detailed electrical transport studies under pressure on single crystals of URu2Si2 confirm that the zero- temperature critical field is suppressed smoothly towards an extrapolated critical pressure of 15 kbar, which also corresponds to the accepted critical pressure of the hidden order phase. Improving on previous work on polycrystalline samples, studies of single crystals of URu2-xRexSi2 have provided more precise tracking of the suppression of both the hidden order phase at low doping and the ferromagnetic phase at intermediate Re concentrations