Crossover from one-dimensional copper-oxygen chains to two-dimensional ladders charge transport in (La,Y)y(Sr,Ca)14-yCu24O41 (original) (raw)
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Physical Review B, 2008
The charge transport in the copper-oxygen chain/ladder layers of ͑La, Y͒ y ͑Sr, Ca͒ 14−y Cu 24 O 41 is investigated along two crystallographic directions in the temperature range from 50 to 700 K and for doping levels from y Ϸ 6 ͑number of holes n h Ͻ 1͒ to y =0 ͑number of holes n h =6͒. A crossover from a one-dimensional hopping transport along the chains for y Ն 3 to a quasi-two-dimensional charge conduction in the ladder planes for y Շ 2 is observed. This is attributed to a partial hole transfer from chains to ladders when the hole doping exceeds n h Ϸ 4 and approaches fully doped value n h = 6. For y Շ 2 a weak dielectric relaxation at radio frequencies and a microwave mode are detected, which might be recognized as signatures of a charge-density wave phase developed at short length scales in the ladder planes.
Variable-range hopping conductivity in the copper-oxygen chains of La3Sr3Ca8Cu24O41
Physical Review B, 2003
We show that the spin chain/ladder compound La3Sr3Ca8Cu24O41 is an insulator with hopping transport along the chains. In the temperature range 35 -280 K, DC conductivity σDC(T ) follows Mott's law of variable-range hopping conduction; the frequency dependence has the form σ(ν, T ) = σDC(T )+A(T )·ν s , where s ≈ 1. The conduction mechanism changes from variable-range hopping to nearest-neighbor hopping around Tc = 300 K. The chain array thus behaves like a one-dimensional disordered system. Disorder is due to random structural distortions of chains induced by irregular coordination of the La/Sr/Ca ions.
ONE-DIMENSIONAL HOPPING CONDUCTIVITY OF THE SPIN-LADDER CaCu 2 O 3 SINGLE CRYSTALS
2008
Resistivity, ρ, of the spin-ladder compound CaCu2O3 is investigated between T ~ 130− 450 K. The ρ (T) data exhibit an activated dependence characterized by a nearest-neighbor hopping followed by a variable-range hopping (VRH) regime when T is decreased. The observed VRH conductivity on the low-temperature interval obeys the law ln ρ ~ T . This law can be explained and the correct matching of the characteristic energy and length scales can be found by treating CaCu2O3 as a three-dimensional array of quasi-one-dimensional electron crystals. Spin-ladder compounds attracted much attention during recent years [1]. A typical compound, SrCu2O3 has a layered structure consisting of the linear Cu−O−Cu−O−rows (“legs”) along the b direction and the short Cu−O−Cu “rungs” along the a direction, having a two-leg “ladder” structure within each layer in the (a, b) plane. Structure of CaCu2O3 is similar to SrCu2O3 but consists of the zigzag Cu2O3 chains (Cu and O atoms do not form a planar network) ...
Physical Review Letters, 2007
We use microprobe Angle-Resolved Photoemission Spectroscopy (µARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor, YBa2Cu4O8. In the CuO2 planes, a two dimensional (2D) electronic structure with nearly momentum independent bilayer splitting is observed. The splitting energy is 150 meV at (π,0), almost 50% larger than in Bi2Sr2CaCu2O 8+δ and the electron scattering at the Fermi level in the bonding band is about 1.5 times stronger than in the antibonding band. The CuO chains have a quasi one dimensional (1D) electronic structure. We observe two 1D bands separated by ∼ 550meV: a conducting band and an insulating band with an energy gap of ∼240meV. We find that the conduction electrons are well confined within the planes and chains with a non-trivial hybridization. PACS numbers: 74.25.Jb, 74.72.Hs, 79.60.Bm
Anisotropic charge modulation in ladder planes of Sr14−xCaxCu24O41
Physical Review B, 2005
The charge response of the ladders in Sr14−xCaxCu24O41 is characterized by dc resistivity, low frequency dielectric and optical spectroscopy in all three crystallographic directions. The collective charge-density wave screened mode is observed in the direction of the rungs for x=0, 3 and 6, in addition to the mode along the legs. For x=8 and 9, the charge-density-wave response along the rungs fully vanishes, while the one along the legs persists. The transport perpendicular to the planes is always dominated by hopping.
Phase diagrams of (La,Y,Sr,Ca) 14 Cu 24 O 41 : Switching between the ladders and the chains
Journal de Physique IV (Proceedings), 2005
The most comprehensive charge response study of the intrinsically hole doped, spin-chain and spin-ladder composites is overviewed. Results of dc and electric-field-dependent resistivity, low frequency dielectric, and optical spectroscopy in all crystallographic directions are used to build phase diagrams of the underdoped materials (hole count= 6 − y per formula unit, f.u.) and of the fully doped , 6 holes per f.u. The underdoped materials are insulators with hopping transport along the chains, which behave as a onedimensional disordered system. For the fully doped materials the charge transport switches to the ladders due to transfer of holes from the chains. Two-dimensional (2D) charge-density wave (CDW) ground state is formed, i.e. besides CDW phason response along the ladders for 0 ≤ x ≤ 9, we also found it along the ladder rungs for x ≤ 6. However, CDW sliding conductivity, as observed in the standard CDW materials, is not observed in either of directions. Normal to the ladder planes no CDW response was found, and transport is presumably hopping-like. For the first time in any system, CDW response away from the principal direction was identified. For x>9 both CDW in ladders and CO in chains are supressed.
Charge and spin degrees of freedom in A -site ordered YCu3Co4O12 and CaCu3Co4O12
Physical Review B, 2021
Using soft x-ray absorption spectroscopy we were able to determine unambiguously the charge and spin states of the transition metal ions in stoichiometric YCu 3 Co 4 O 12 and CaCu 3 Co 4 O 12. The trivalent and low-spin nature of both the Cu and Co ions in YCu 3 Co 4 O 12 makes this correlated system to be effectively a nonmagnetic band semiconductor. The substitution of Y by Ca produces formally tetravalent Co ions but the doped holes are primarily on the oxygen ligands. Concerning the spin degrees of freedom, the trivalent Co ions in YCu 3 Co 4 O 12 remain low spin upon the Y-Ca substitution, very much unlike the La 1-x Sr x CoO 3 system. The tetravalent Co ions in CaCu 3 Co 4 O 12 are interestingly also in the low-spin state, which then explains the good electrical conductivity of CaCu 3 Co 4 O 12 since charge exchange between neighboring Co 3+ and Co 4+ ions will not be hampered by the spin-blockade mechanism that otherwise would be in effect if the Co 4+ and Co 3+ spin quantum numbers were to differ by more than one-half. We infer that the stability of the Co low-spin state is related to the very short CoO bond lengths.
Electric transport in YBa2Cu3O7-δ/La1/3Ca2/3MnO3/La2/3Ca1/3MnO3 planar-type
physica status solidi (c), 2005
Current transport through thin antiferromagnetic barriers has been studied with respect to its dependence on temperature and voltage in planar YBa 2 Cu 3 O 7-δ (∼ 100 nm)/La 1/3 Ca 2/3 MnO 3 (∼7 nm)/La 2/3 Ca 1/3 MnO 3 (∼ 80 nm) heterojunctions with c-axis oriented YBa 2 Cu 3 O 7-δ layer. Current-voltage (I-V) measurements were made on test junctions with a standard area of 20×40 µm 2 in a four-terminal configuration. The dynamic conductance G ≡ dI/dV versus voltage displayed a pronounced zero-bias conductance peak in the low-voltage range, with its size being strongly dependent on the temperature; the height of this peak increases as the temperature decreases. For a given temperature, an abrupt conductance decreasing is observed toward a bit higher values of the voltage. The low values of the junction resistance indicated that direct metallic conduction is shorting the tunneling current.
Physica C: Superconductivity, 1998
63 Cu and 17 O NMR measurements in the normal and superconducting states of Tl Ba Ca Cu O with different d 2 2 2 3 1 0 yd Ž opt. opt are reported. In the overdoped Tl2223 sample with T s 117 K T s 123 K and dd different temperature c c 1 dependencies of the Knight shift 17 K are revealed for inequivalent CuO layers. For the inner CuO layer with the square 2 2 oxygen coordination of Cu the decrease of 17 K with temperature is more gradual. In going towards the underdoped Tl2223 with T s 104 K and d) d opt the changes of 63,17 K with temperature are found to be the same for both types of copper c 2 layers. The quadrupole coupling constants for copper and oxygen from different CuO layers were obtained. From the 2 variations with doping of the valence contribution to the electric field gradient at copper sites, we estimate both the hole numbers at Cu and oxygen sites and the real concentration of mobile hole carriers n in each of inequivalent CuO layers. In h 2 Ž the overdoped Tl2223 sample the charge density in the inner layer differs from the one in the outer plane with five-fold. oxygen coordination for Cu. Our results show that the inhomogeneity of the charge distribution disappears in the underdoped regime. The results are compared with calculations of the charge distribution among the CuO planes in 2 w Ž. x multilayered cuprates reported by Haines and Tallon E.M.