The structural transition of AlN nanowires was investigated under pressures up to 51.1GPa by in situ angle dispersive high-pressure x-ray diffraction using synchrotron radiation source and a diamond anvil cell. A pressure-induced wurtzite to rocksalt phase transition starts at 24.9GPa and completes at 45.4GPa. The high-pressure behaviors of AlN nanowires differing from the bulk and nanocrystal AlN might arise from the intrinsic geometry in nanowires.

The high-pressure and high-temperature behaviors of anhydrite (CaSO4) are studied up to 53.5 GPa and 1800 K using double-sided laser heating Raman spectroscopy and x-ray diffraction in diamond anvil cells. The evidence of phase transition from an anhydrite structure to the monazite type was observed at about 2 GPa under cold compression. Another phase transition and a change in color of the sample from transparent to black have been also observed at a pressure of 33.2 GPa after laser heating. The new phase after laser heating persists to 53.5 GPa and 1800 K.

A new high-pressure phase of solid calcium hydride at room temperature was discovered by in situ Raman scattering experiments with a diamond anvil cell. The phase transition was found to start at ∼15.5 GPa and complete at ∼21 GPa, and it is reversible with a hysteresis to ∼12 GPa, when the pressure was released. Moreover, the high-pressure phase was found to be stable up to at least 42 GPa. First-principles calculations were performed to assign the measured Raman modes at zero pressure accurately and to understand the pressure dependence of the Raman frequency shift before the transition.

We present dynamic nuclear polarization (DNP) in the simplest pseudospin quantum Hall ferromagnet (QHF) of an InSb two-dimensional electron gas with a large g factor using tilted magnetic fields. The DNP-induced amplitude change of a resistance spike of the QHF at large current enables observation of the resistively detected nuclear magnetic resonance of the high nuclear spin isotope 115 In with nine quadrupole splittings. Our results demonstrate the importance of domain structures in the DNP process.The nuclear spin relaxation time T 1 in this QHF was relatively short (~ 120 s), and almost temperature independent.

The spin polarization (P) of high-density InSb two-dimensional electron systems (2DESs) has been measured using both parallel and tilted magnetic fields. P is found to exhibit a superlinear increase with the total field B. This P-B nonlinearity results in a difference in spin susceptibility between its real value χ s and χ gm ∝ m * g * (m * and g * are the effective mass and g factor, respectively) as routinely used in experiments. We demonstrate that such a P-B nonlinearity originates from the linearly P-dependent g * due to the exchange coupling of electrons rather than from the electron correlation as predicted for the low-density 2DES. 71.27.+a, 73.43.Qt Direct experimental evidence of the P-B nonlinearity has so far been reported in low-density GaAs 2DESs with a relatively large r s ~ 5.6 at P < 0.5 [11], where the correlation energy is believed to determine the P-B nonlinearity [11,12]. We here, however, present a similar nonlinear P-B dependence via a high-density InSb 2DES with a small r s ~ 0.2. The large g * (over 39 in magnitude) of the InSb 2DES makes the P = 1 state achievable at easily accessible fields and the magnetization curve (P vs. its corresponding field B p ) observable over a wide range of P from 0.07 to 1. P is found to be superlinear in B p , which is analogous to the findings in Ref. 11. This P-B nonlinearity is fit well by a simple empirical equation. Note that χ gm calculated by this equation can also be used to fit the non-monotonic n 2D -χ gm data in Ref. 11. However, the P-B nonlinearity in the high-density specimen does not arise from the electron correlation because of the small r s . Further experiments demonstrate that this P-B nonlinearity is attributed to a linear P dependence of g * . PACS: Samples and methodsUnless otherwise noted, the employed InSb 2DES in a Hall bar (80 μm ×30 μm) is confined to a 30 nm wide InSb quantum well (QW) with δ-doped Al 0.09 In 0.91 Sb barriers on each side of the well [15].The parallel and tilted-field measurements were performed at 200 mK in a dilution refrigerator with an in situ rotator. The tilt angle θ between B and the sample normal (inset, figure 1(a)) was determined from the Hall resistance with an accuracy of at least 0.1 ○ . A low-frequency AC lock-in technique (13.3 Hz, 3 nA) was used to measure the longitudinal resistance R xx . Magnetotransport measurements gave n 2D = 1.83 × 10 15 m -2 and an electron mobility of μ = 14.3 m 2 /Vs in this sample. Experimental results and discussionAs shown in the inset of figure 1(b), the energy space between Landau levels (LLs) with spin-up (↑) and spin-down (↓) electrons is enhanced with increasing the tilted angle. Because the cyclotron energy (where is the reduced Planck's constant h, * / m eB E perp C