Optimally doped silver selenide and silver telluride exhibit linear positive magnetoresistance over decades in magnetic field and on a scale comparable to the colossal magnetoresistance compounds. We use hydrostatic pressure to smoothly alter the band structure of Ag-rich and Ag-deficient samples of semiconducting Ag 26d Te of fixed stoichiometry and disorder. We find that the magnetoresistance spikes and the linear field dependence emerges when the bands cross and the Hall coefficient changes sign. DOI: 10.1103/PhysRevLett.88.066602 PACS numbers: 72.20.My, 72.15.Gd, 72.80.Jc The magnetoresistive response of a material can open a window into the dispersion and dynamics of the charge carriers, and in opportune cases can be exploited for technological use. The magnetoresistance at small fields is usually quadratic because of the vector nature of the magnetic field, and is expected to saturate when the applied field becomes large [1]. Under special circumstances, the resistivity can grow linearly with applied field [2]. High-field linear magnetoresistance can be found in polycrystalline materials with open orbits in the Fermi surface [3], in inhomogeneous materials where the tensor components of the resistivity can be mixed [4], and in the extreme quantum limit where one Landau level dominates (e.g., bismuth) [5 -7].A few years ago, positive linear magnetoresistance was observed from magnetic fields of mT to T in the silver chalcogenides, Ag 2 Se and Ag 2 Te [8]. Stoichiometric material remains indifferent to the application of a magnetic field [9], but small amounts of excess silver or excess Se/Te lead to changes in the resistivity of many hundreds of percent in fields of a few T. This large magnetic response is comparable in absolute magnitude to that observed in manganese perovskites, the so-called colossal magnetoresistance materials, but occurs here in intrinsically nonmagnetic materials that can be fabricated both in bulk and as thin films [8,[10][11][12][13].The unusually large range of linearity observed in some samples of Ag 21d Se and Ag 21d Te, the failure of the magnetoresistance to saturate even when the product of the cyclotron frequency and the scattering time, v c t, greatly exceeds one, and the robust absolute scale of the response combine to make the silver chalcogenides especially inviting materials to illuminate the mechanisms of linear magnetoresistance. In particular, Abrikosov has proposed that an essential ingredient for "quantum linear magnetoresistance" in both the small and large field limits is a semiconducting gap that approaches zero, with an energy dispersion that becomes linear in momentum [2,14].In this Letter, we use hydrostatic pressure to tune the band gap of both p-type and n-type samples of silver telluride of fixed stoichiometry and disorder. Under pressure, hole-dominated transport can be transformed into electron-dominated transport, and barely metallic n-type samples can be converted into good metals. We find for p-type material that both the linear magnetoresistance a...

The electrical resistivity and thermopower S of pure liquid silicon and pure liquid germanium have been carefully measured. For silicon, a new containment material was used, namely high-density graphite. This graphite has a low thermopower ( at ) a high resistivity ( at ), and little or no reaction with Si, making it an ideal containment material. The results for each liquid show a metallic value of resistivity, a small but positive temperature coefficient of the resistivity and a small thermopower. In particular, for liquid Si, , and and, for liquid Ge, , and ; all values are for the respective melting temperatures of Si and Ge. We also report a calculation of the resistivity of each liquid, using the Ziman formalism, with a recent pseudopotential and an experimental structure factor. Both our experimental and our calculated results are compared with other work.

We compare the large magnetoresistive response of slightly nonstoichiometric Ag2±δTe for a wide range of hole (p⩽8×1017 cm−3) and electron (n⩽4×1018 cm−3) carrier densities. In the p-type material alone, a characteristic peak in the resistivity ρ(T,H) is dramatically enhanced and moves to higher temperature with increasing magnetic field, resulting in a high field (H∼5 T) magnetoresistance that is sizeable even at room temperature. By contrast, n-type specimens are geared for low-field (H<0.1 T) applications because of a striking linear field dependence of the magnetoresistance that appears to be restricted to the Ag-rich materials.

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In this paper we report measurements of the drift velocity of electrons in liquid Ar and Kr as a function of temperature, pressure, and electric field strength. The experimental findings are as follows: (a) At low temperatures ( <115°K) in liquid Ar, the mobility of the electron (^400 cm 2 V" 1 sec -1 ) decreases with increasing temperature and increases with increasing pressure. In this region the electron drift velocity is linear in the electric field strength (from -100 to -200 V/cm). (b) At high temperatures (> 115°K) in liquid Ar and at all temperatures in liquid Kr the electron drift velocity (4-20 X10 4 cm/sec) at electric field strengths from -50 to -150 V/cm increases with increasing temperature. There may be a maximum in the electron drift velocity-temperature profile of liquid Kr. In this region the drift velocity is not linear in the electric field strength. It is demonstrated that an elementary scattering theory (with several variants for the scattering cross section) provides a reasonable zeroth-ordex description of the electron mobility in liquid Ar in the low-field, low-temperature (<115°K) region. The theory incorporates the effects of coherence in the electron scattering from nearby atoms into the cross section of a modified Boltzmann equation. The magnitude of the mobility and the pressure and temperature dependence (85-115°K in liquid Ar) of the mobility are all reproduced to better than a factor of 2. It is found that the electron velocity distribution is not thermal and that the mean electron energy may be as large as 0.5 eV, even when the electric-field strength is as low as 100 V/cm. By numerical calculation based on the elementary scattering theory, we find the onset of nonlinearity in the electric-field dependence of the electron drift velocity at £« 1 V cm -1 in disagreement with the experimental findings described in (a). The anomalous rise of the drift velocity per unit field in liquid Ar above 115°K, and at all temperatures in liquid Kr, intuitively suggests that there may be a Ramsauer minimum in the effective electron-atom scattering cross section in the liquid. Within the framework of the elementary theories considered, we have, at present, no explanation for the anomalous temperature dependence of the electron drift velocity in liquefied Ar and Kr. 7 H. T. Davis, S.