Physics
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The Physics department is committed to education and research in physics, the study of the fundamental universal laws that govern the behavior of matter and energy, and the exploration of the consequences and applications of those laws. Our department is widely known for its excellent teaching and student mentoring. Our department plays an important role in the university’s Core Curriculum. We have strong academic programs with several options for undergraduate physics majors, leading to the B.S. degree, as well as graduate curricula leading to the M.S. and Ph.D. degrees. Our research groups span a variety of fields within physics. Our principal concentrations are in Astrophysics, Relativity, Gravitation and Cosmology, Condensed Matter Physics, Lasers and Optics, Physics Education, Solar Physics, and the Space Science and Engineering Lab.
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Item Thermal Properties of the Frustrated Rb0.52(ND4)0.48D2PO4 System at Low Temperatures(1985-01) Lawless, W. N.; Schmidt, V. HugoSpecific heat and thermal conductivity data, 1.5–35 K, are reported on the mixed (frustrated) ferroelectric-antiferroelectric crystal Rb0.52(ND4)0.48D2PO4. A glasslike linear term in the specific heat is resolved below 5 K and ascribed to random electric fields caused by the random distribution of Rb ions, in good agreement with the theory of McWhan et al. A maximum in C/T3 at 13.5 K is attributed to dispersionless motions of the deuterium ions, by analogy with KDP. In contrast to the specific heat, the thermal conductivity is not glasslike, displaying a maximum at 12.5 K of 37 mW cm-1K-1. At lower temperatures, the behavior of the thermal conductivity is tentatively ascribed to resonant phonon scattering from the Rb–ND4 system. The Debye temperature for the crystal is 303 K, in reasonably good agreement with extrapolations based on θD for KDP.Item Slater-senko model for CsH2PO4(1984-04) Schmidt, V. HugoThis model for CsH2PO4 considers all six Slater H2PO4 configurations and employs the Senko long-range interaction to obtain a ferroelectric transition above 0 K. Model predictions are compared with experimental results for susceptibility, spontaneous polarization, and correlation length.Item Pressure dependence of ferroelectric transition temperature in TSCC(1980-08) Windsch, W. Wolfgang; Schmidt, V. HugoOur measured values of the ferroelectric transition temperature Tc in tris-sarcosine calcium chloride (TSCC) for pressure p between 0 and 2.1 kbar obey the relation Tc = a + bp + cp2, where a = (128.6 ± 0.2)K,b = (+13.2 ± 0.4)K/kbar and c = (-0.5 ± 0.2)K/(kbar)2.Item Anomalies of hypersound velocity and attenuation in ferroelectric tris-sarcosine calcium chloride (TSCC) for small-angle and right-angle Brillouinscattering and Brillouin backscattering(1986-07) Wang, J. T.; Schmidt, V. HugoThe Brillouin spectra of ferroelectric tris-sarcosine calcium chloride have been observed using small-angle and right-angle scattering and also backscattering. For different-frequency phonons along the same direction, analogous anomalies in the sound velocity and the attenuation are seen. The smallest angle we have achieved is 7.48°. The temperature and frequency dependences of the sound velocity are discussed. The fact that the linewidth maximum for [001] phonons occurs somewhat below Tc seems to indicate that the anomalies are due to piezoelectric coupling induced by spontaneous polarization below Tc. For [010] phonons the elementary relaxation times which relate to the energy are estimated as τE0=5.25×10−13 sec above Tc and τE0=3.32×10−12 sec below Tc. The phonon attenuations are also estimated and compared with the observed ones. For the [001] phonons the elementary relaxation time is estimated as τ0=5.25×10−14 sec, in good agreement with the value obtained from right-angle Brillouin scattering.Item Pressure dependence of proton glass freezing in Rb1−x (NH4)x H2PO4(1986-08) Samara, G.A.; Schmidt, V. HugoStudies of the frequency-dependent dielectric properties of a Rb0.52(ND4)0.48D2PO4 (72% deuterated) crystal have shown that the deuteron glass-freezing temperature Tg is suppressed by hydrostatic pressure at a rate of -2.0 K/kbar. This is explained in terms of the influence of pressure on the hydrogen-bond potential. It is suggested that the glassy state should be completely suppressed (i.e., Tg→0 K) at a pressure of less than 10 kbar in undeuterated crystals of similar composition.Item EPR determination of three-dimensional correlations below the ferroelectric phase transition in pseudo-one-dimensional CsH2PO4:Cu2+(1986-11) Waplak, S.; Schmidt, V. Hugo; Drumheller, John E.The polarization fluctuations of ferroelectric CsH2PO4 above Tc are generally classified as a quasi-one-dimensional phenomenon. The temperature dependence of the EPR line splitting of the S=1 state of the Cu2+ tetramer, however, exhibits a critical exponent below Tc of β=0.5 indicating that the correlations associated with the order parameter are three dimensional below Tc.Item Proton-glass dielectric behavior of a Rb0.52(ND4)0.48D2PO4 crystal(1984-09) Schmidt, V. Hugo; Waplak, S.; Hutton, Stuart L.; Schnackenberg, P. T.The c axis dielectric permittivity at 1 kHz was measured for a 71.4 at.% deuterated crystal of Rb0.52(ND4)0.48D2PO4 from 4 to 300 K. The permittivity follows, down to 150 K, a Curie-Weiss law with a Curie temperature of 0 K. Below this temperature the susceptibility rounds off to a broad maximum at 80 K, and below 50 K, starts decreasing rapidly. Between 25 and 40 K, the inverse susceptibility obeys a Curie-Weiss law which extrapolates to zero at 43 K. At 4 K, the relative permittivity flattens out to a value of 11.5. The results show general agreement with predictions of a Landau model giving a second-order transition to an antiferroelectric state at 43 K, but the rounding of the susceptibility peak over a very wide temperature range agrees better with predictions of a model which considers the asymmetry of the typical hydrogen bond caused by the crystal being only partly ammoniated. Permittivity results of Courtens and of Iida and Terauchi for undeuterated crystals with 35% and 60% ammonium, respectively, are also compared with predictions of this second model.Item Brillouin scattering study of the ferroelectric phase transition in tris-sarcosine calcium chloride(1985-01) Hikita, T.; Schnackenberg, P. T.; Schmidt, V. HugoBrillouin spectra from longitudinal phonons in ferroelectric tris-sarcosine calcium chloride propagating along [100], [010], and [001] have been measured as functions of temperature. Large anomalies were found in the Brillouin shift and linewidth in the [100] and [001] phonons. These anomalies are interpreted as arising from the linear coupling of the polarization and the phonons. From the temperature where the linewidth is maximum, the relaxation time of the polarization fluctuations is estimated to be τ=3.1×10−12/(Tc-T) sec, where Tc is the ferroelectric transition temperature. We also observed anomalies in Brillouin shift and linewidth of the [010] phonons which propagate along the ferroelectric b axis. These anomalies are interpreted as coming from electro- strictive coupling. The energy-relaxation time was estimated to be τE=2.5×10−10/(T-Tc) sec in the paraelectric phase and τE=1.0×10−9/(Tc-T) sec in the ferroelectric phase, by comparing our Brillouin results with those of the ultrasonic measurements.Item High-pressure–low-temperature apparatus for NMR study of phase transitions(1982-07) Schuele, Paul J.; Schmidt, V. HugoAn apparatus has been developed for nuclear‐magnetic‐resonance (NMR)measurement of relaxation times in solids at hydrostaticpressures to 7 kbar and temperatures down to 77 K. Sample temperature can be controlled accurately with ±2 mK stability allowing measurement of dynamic phenomena very near phase transitions. The high‐pressure vessel is equipped with additional electrical feedthroughs so that dielectricmeasurements can be carried out concurrently, providing additional information on ferroelectric phase transitions.