We have made a high-resolution photoemission study of La 22x Sr x CuO 4 in a wide hole concentration (x) range from a heavily overdoped metal to an undoped insulator. As x decreases, the spectral density of states at the chemical potential (m) is suppressed with an x dependence similar to the suppression of the electronic specific heat coefficient. In the underdoped region, the spectra show a pseudogap structure on the energy scale of 0.1 eV. The width of the pseudogap increases with decreasing x following the x dependence of the characteristic temperatures of the magnetic susceptibility and the Hall coefficient. [S0031-9007(98)06985-3] PACS numbers: 71.30. + h, 74.72.Dn, 74.25.Jb, 79.60.Bm In order to understand the mechanism of hightemperature superconductivity in doped cuprates, a central issue has been the evolution of the electronic structure with hole doping near the filling-control metal-insulator transition (MIT). In spite of extensive photoemission studies, it still remains unclear how the electronic structure evolves, especially between underdoped metal and antiferromagnetic insulator. For a systematic study of the doping dependence near the MIT, La 22x Sr x CuO 4 (LSCO) is a suitable system. It has the simplest crystal structure with single CuO 2 layers and the hole concentration in the CuO 2 plane is well controlled over a wide range and uniquely determined by the Sr concentration x (and small oxygen nonstoichiometry). So far photoemission studies of high-T c cuprates were concentrated on Bi 2 Sr 2 CaCu 2 O 8 (BSCCO) and YBa 2 Cu 3 O 72y (YBCO) systems. With the LSCO system, one can investigate the electronic structure of the CuO 2 plane continuously from the heavily overdoped limit (x ϳ 0.35) to the undoped insulator (x 0) in a single system.Recently, in underdoped cuprates a "normal-state gap" behavior above T c has been observed by angle-resolved photoemission spectroscopy (ARPES) in BSCCO [1] and a "spin-gap behavior" by NMR in YBCO [2]. The magnitude of the normal-state gap is of the same order as the superconducting gap at optimal doping. Meanwhile, underdoped cuprates have characteristic temperatures which are considerably higher than T c in the uniform magnetic susceptibility [3], the electronic specific heat [4], the Hall coefficient [5], and the electrical resistivity [3]. All these characteristic temperatures show similar behaviors in LSCO: they increase from ϳ300 K at optimal doping x ϳ 0.15 to ϳ600 K at x ϳ 0.1 for the LSCO system, suggesting a pseudogap-type electronic structure. In addition, it can be reconciled only if a pseudogap is opened at the chemical potential that both the electronic specific heat coefficient g [4,6] and the chemical potential shift with doping [7] are suppressed towards the MIT. To obtain a full picture of the evolution of those "gaps," it is also necessary to know the total density of state (DOS), which is most directly observed by angle-integrated photoemission spectroscopy (AIPES). In the present study, we have performed high-resolution AIPES measurements...
The magnetoelectric effect in bulk matter is of growing interest both fundamentally and technologically. Since the beginning of the century, the magnetoelectric effect has been studied intensively in multiferroic materials. However, magnetoelectric phenomena in materials without any (anti-)ferroic order remain almost unexplored. Here we show the observation of a new class of bulk magnetoelectric effect, by revisiting elemental trigonal tellurium. We demonstrate that elemental tellurium, which is a nonmagnetic semiconductor, exhibits current-induced magnetization. This effect is attributed to spin splitting of the bulk band owing to the lack of inversion symmetry in trigonal tellurium. This finding highlights magnetoelectricity in bulk matter driven by moving electrons without any (anti-)ferroic order. Notably, current-induced magnetization generates a magnetic field that is not circular around but is parallel to the applied current; thus, this phenomenon opens a new area of magnetic field generation beyond Ampere’s law that may lead to industrial applications.
We report the observation of a Hall effect driven by orbital resonance in the quasi-1-dimensional (q1D) organic conductor (TMTSF)2ClO4. Although a conventional Hall effect is not expected in this class of materials due to their reduced dimensionality, we observed a prominent Hall response at certain orientations of the magnetic field B corresponding to lattice vectors of the constituent molecular chains, known as the magic angles (MAs). We show that this Hall effect can be understood as the response of conducting planes generated by an effective locking of the orbital motion of the charge carriers to the MA driven by an electron-trajectory resonance. This phenomenon supports a class of theories describing the rich behavior of MA phenomena in q1D materials based on altered dimensionality. Furthermore, we observed that the effective carrier density of the conducting planes is exponentially suppressed in large B, which indicates possible density wave formation.
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