Maple Group: Physics of Correlated Electron Materials

The focus of our research is the physics of correlated electron materials. We study intermetallic compounds and oxides of transition metal, rare earth, and actinide elements, at low temperatures, in high magnetic fields, and at high pressures. Our laboratory at UCSD is equipped with extensive facilities for both the growth and characterization of novel d- and f-electron materials. Phenomena such as superconductivity, magnetism, heavy fermion behavior, and non-Fermi liquid behavior are fundamentally related to the d- and f-orbital electrons of these elements. We highlight some of our recent work below - a more complete list exists on our projects page.
Navigation background image: crystals of Ce0.01Y0.99RhIn5
Research Highlights

When Re is substituted for the Ru in URu2-xRexSi2, the hidden order phase is suppressed, and ferromagnetic order arises at intermediate concentrations. We have grown single crystals to study the transformation of the ordered phases and the non-Fermi liquid behavior that is observed in the vicinity of the onset of ferromagnetism, searching for indications of quantum criticality.
To URuReSi<sub>2</sub> Page

To URu<sub>2</sub>Si<sub>2</sub> Under Pressure Page The pressure phase diagram of URu2Si2 was investigated to identify the relationship between the superconducting and hidden order phases. The properties of the superconducting state were studied as a function of both temperature and magnetic field, but no signature of a transition from hidden order to large moment antiferromagnetism was observed.

Single crystals of the filled skutterudite compound PrOs4As12 have been successfully grown and were found to order magnetically at very low temperatures, below 2.3 K. In addition to this antiferromagnetic ground state, the material exhibits a different, as yet unidentified, ordered state in applied magnetic fields. Measurements have also established that PrOs4As12 is a heavy fermion compound, which behaves like its constituent electrons are hundreds of times heavier than free electrons.
To PrOs4As12 Page

To PrOs4Sb12 Page The filled skutterudite PrOs4Sb12 was recently discovered in our laboratory to be the first Pr-based heavy fermion (HF) superconductor, with a Tc of 1.85 K. We are currently investigating the series Pr(Os1-xRux)4Sb12. As Ru is substituted for Os, Tc decreases nearly linearly with substituent concentration and exhibits a minimum with a value of Tc = 0.75 K at x = 0.6, suggesting that two types of superconductivity are competing with each other.

CeRh1-xCoxIn5 is a heavy-fermion antiferromagnet that displays superconductivity when tuned by pressure or Co concentration. Higher Co concentrations result in a decrease in AFM and a quantum critical point around x = 0.8. Applied pressure results in a similar decrease in AFM and also leads to quantum critical points. The quantum critical point in pressure is seen to decrease towards zero as concentration is increased, consistent with a zero pressure QCP at x = 0.8.
To CeRhCoIn5 Page

To MgB2 Page We found evidence for the co-existence of a first order vortex-lattice melting transition and a continuous vortex-glass melting transition at a lower temperature in high purity twinned YBa2Cu3O7-δ single crystal samples grown in BaZrO3 crucibles. Analysis of the data strongly indicates the vortex matter in the single crystal is inhomogeneous. This scenario is supported by the observation of a vortex-lattice melting at a temperature separating two vortex-glass states with different critical exponents.

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