Particle-hole symmetry in the antiferromagnetic state of the cuprates

Abstract

In the layered cuprate perovskites, the occurrence of high-temperature superconductivity seems deeply related to the unusual nature of the hole excitations. The limiting case of a very small number of holes diffusing in the antiferromagnetic (AF) background may provide important insights into this problem. We have investigated the transport properties in a series of crystals of YBa2Cu3Oy, and found that the temperature dependencies of the Hall coefficient RH and thermopower S change abruptly as soon as the AF phase boundary is crossed. In the AF state at low temperatures T, both RH and S are unexpectedly suppressed to nearly zero over a broad interval of T. We argue that this suppression arises from near-exact symmetry in the particle-hole currents. From the trends in RH and S, we infer that the symmetry is increasingly robust as the hole density x becomes very small (x Ӎ 0.01). We discuss implications for electronic properties both within the AF state and outside.I n the layered cuprate perovskites, high-temperature superconductivity appears when a moderate density of holes are introduced into the CuO 2 planes by chemical doping. The parent (undoped) compound is a Mott insulator with a spin-1 ⁄2 moment residing on each Cu ion in the plane. Below the Néel temperature, long-range, three-dimensional (3D) antiferromagnetism is stable. The introduction of holes destroys the static 3D antiferromagnetic (AF) order, and superconductivity appears when the relative hole population x exceeds Ϸ0.05 per Cu ion. In the quest to understand cuprate superconductivity, it has long been recognized that determining the nature of the itinerant hole moving in a sea of disordered spin-1 ⁄2 moments with short-range AF order is an essential step. Because semiclassical approximations are not reliable for this spin-1 ⁄2 system, the problem has remained intractable despite a decade of theoretical effort (1-6). In the dilute limit (x Ͻ 0.05), the hole has been variously described as a ''holon'' moving in a resonating valence bond liquid (1), or an excitation dressed with a spiral spin-current backflow (2), or as a charge trailing a phase string (4).In this limit, the signals from the itinerant carriers become increasingly difficult to resolve from background signals, especially in experiments that ''see'' all of the valence electrons in the sample. Transport experiments, which probe directly the itinerant holes without background problems, would appear to have a valuable role to play. To date, however, the available transport data in the very underdoped limit come almost entirely from the single-layer cuprate La 2-x Sr x CuO 4 (LSCO). The resistivity and Hall results in LSCO do not appear to be qualitatively different from those in the moderately underdoped regime (0.05 Ͻ x Ͻ 0.13; refs. 7 and 8). However, because doping by Sr substitution creates strong disorder, there is good reason to suspect that results in LSCO reflect the properties of the disorder-dominated CuO 2 plane.Doping-induced disorder is much less of a factor in the bilayer ...

Dynamics of Metallic Stripes in Cuprates

“…The HEMIR has not been clearly resolved by reflectivity in YBa 2 Cu 3 O 6+δ (YBCO), but a strong broad feature at the right energy appears in photodoped transmission experiments [8]. As far as we know no microscopic explanation of the HEMIR exists so far.Another important aspect of layered cuprates that has emerged in the last years is the rearrangement of doped holes in antiferromagnetic (AF) domain walls[9, 10, 11, [11,12,13,14] (d is the distance between charged stripes in units of the lattice constant), chemical potential [18,19], and transport experiments [20,21] as a function of doping have been explained in a parameter free way [16].In this work we investigate the optical conductivity in terms of linear excitations around the metallic meanfield stripes of Ref. [16].…”

“…Another important aspect of layered cuprates that has emerged in the last years is the rearrangement of doped holes in antiferromagnetic (AF) domain walls[9, 10, 11, [11,12,13,14] (d is the distance between charged stripes in units of the lattice constant), chemical potential [18,19], and transport experiments [20,21] as a function of doping have been explained in a parameter free way [16].…”

Particle-hole symmetry and transport properties of the flux state in underdoped cuprates

“…However this does not mean that the electronic state in the antiferromagnets is fully understood. Compared with the triplet channel of the two-particle correlation functions, the single particle properties such as the angle resolved photo-emission spectra (ARPES) [2], and the singlet channel correlation functions such as the charge transport properties [3,4,5,6,7,8] still remain controversial. In fact, there are two different pictures for it.…”

“…Another interesting clue is that in LSCO the suppression of the Hall effect is observed only in the vertical (horizontal) stripe state while is not in the diagonal stripe state for x < 0.05 [23,24]. Above T N , R H is a decreasing function of temperature, which remains one of the most puzzling features in the normal state properties [3,5,6,25].…”

“…Recently there appeared several experiments on the Hall coefficient R H and the thermopower S in the heavily underdoped cuprates, which raised the issue of particlehole symmetry [6,7,8]. The R H as well as the S show the strong suppression below the Neel temperature T N in some YBCO samples [6] while it is not the case for other samples [7].…”