Experimental Condensed Matter Physics Research at SDSU  
 

Condensed Matter Physics is demonstrably the area of most intense current activity in physics worldwide. The over 30,000 pages of scientific articles published every year by Physical Review B testify to the tremendous ongoing effort in this field, motivated by its fundamental interest as well as its technological relevance.
Condensed Matter Physics is a broad and diverse field, consisting of a unique blend of Classical and Quantum Mechanics, Atomic and Molecular Physics, Chemistry, Quantum Field Theory, Computational and Statistical Physics, as well as Complexity Theory . Because of this fascinating multifacedness, Condensed Matter Physics is intimately connected to many other disciplines, including Biology, Chemistry, Electronics, Geology and Materials Science.
The possibility of easily establishing a contact between theory and experimental observation, renders this field ideal to formulate and test the most advanced theories of the fundamental structure of matter.

The Physics Department at San Diego State University has an active experimental Condensed Matter group consisting of two faculty. Areas of interest include:

• Superfluidity

• Superconductivity

• Magnetism

• Electronic Structure of Metals

• Experiment

  • Prof. Saul Oseroff

  • Prof. Milton Torikachvili

• Theory

  • Prof. Arlette Baljon

• Recent Publications of our group

   

Experimental Condensed Matter

Prof. Saul Oseroff

• We study the magnetic properties of colossal magnetoresistance (CMR) oxides, and compare them with compounds of the same family that do not show CMR. We measure single crystals and powders of 3D perovskites of La_1-xB_xMnO₃ (B = Ca, Sr, Pb), 0 £ x £1, pyrochlores A₂Mn₂O₇ (A = Y, In, and Tl) manganites and (La,Sr)₃Mn₂O₇, a layered manganites. We perform EPR and dc susceptibility measurements up to 1100 K, to investigate the temperature dependence of the EPR linewidth.

• It has been suggested that the Li ions in La₂Ni_0.5Li_0.5O₄ form an ordered superlattice, where individual NiO₄ plaquettes are isolated from each other. The are many open questions regarding this compound. For that reason we are studying by EPR (3 GHz - 220 GHz), Raman scattering, neutron and X-ray diffraction between 4 - 300 K this compound.

• Measurements in hexaborides, AB₆, are being conducted in our lab. It was recently found that Ca_1-xLa_xB₆ has a weak ferromagnetic (WF) moment peaking near x = 0.005, with a Tc of ~ 600 K. A model of a doped excitonic insulator, has been proposed as an explanation. Measurements by EPR, effects of uniaxial stress, microwave-absorption, and magnetization are being conducted in these compounds between 4 K - 1100 K to gain a better understanding of the origin of the WF moment.

• EPR done on SmB₆ doped with Gd³⁺ or Er³⁺ shows a variety of unusual properties. The data was tentatively explained by the Jahn-Teller (J-T) effect. A study by EPR of La_1-xSm_xB₆ and Ca_1-xSm_xB₆ doped with Er and Gd is being carried out. This will make it possible to follow the evolution of the doublet ground state reported in La(Ca)B₆ to the quartet ground state in SmB₆, and the appearance of the Gd²⁺ ground state found in SmB₆.

• CeB₆ has many unexplained properties. The quartet ground state of Ce splits into two doublets. It has been proposed that a J-T distortion split the quartet. EPR experiments up to 220 GHz are planned in La1-xCexB6 and Ca1-xCexB6. The study of these two series may clarify the role-played by the J-T distortion.

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Prof. Milton Torikachvili

My research interest is the study of superconducting and magnetic properties of novel materials. Superconductivity as well as various types of magnetic interactions are remarkable phenomena originated in the electronic interactions in condensed matter. The focus of this research consists mostly on searching for new materials displaying interesting electronic or magnetic properties, synthesizing them, performing a crystallographic analysis, measuring their electronic and magnetic properties, and interpreting the results in terms of theoretical models. The physical properties are determined by means of measurements of electrical resistivity, magnetoresistance, magnetization and neutron scattering, in a wide range of temperatures and magnetic fields. Materials of current interest include intermetallic compounds of rare-earth or actinide elements, manganese oxide based compounds displaying colossal magneto-resistive effects, and high temperature oxide superconductors. The laboratories at SDSU are equipped with several electronic instruments and cryostats, which permit the measurement of electronic and magnetic properties in the 1-300 K temperature range, in magnetic fields up to 5 Tesla. The sample preparation area is equipped with various instruments including an arc furnace operating in an inert atmosphere, and several programmable box and tube furnaces, operating in temperatures as high as 1500 °C. Experiments in very high magnetic fields are performed at the National High Magnetic Field Laboratory in Los Alamos. Neutron scattering experiments are performed at the Intense Pulsed Neutron Source of Argonne National Laboratory, or at the Los Alamos Neutron Science Center of Los Alamos.

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