arXiv subjects

P. H. Hor

Publications and source records attributed to P. H. Hor.

16 recordsLinked to original sources

arXiv2015

On the quantitative determination of hole-concentration in high-temperature cuprate superconductors

We compared four hole-scales that have been used to determine the hole-concentration in high-temperature cuprate superconductors. We show that the hole-scale, $P_{pl}$-scale, based on the thermoelectric power [T. Honma $et$ $al$., Phys. Rev. B70, (2004) 214517.] is quantitatively consistent with spectroscopic probes for many different cuprate materials, while the other hole-scales, based on a well-known dome-shaped $T_c$-curve [M. R. Presland $et$ $al$., Physica C176, 95 (1991)], the $c$-axis lattice parameter [R. Liang $et$ $al$., Phys. Rev. B73, (2006) 180505(R).], and Hall coefficient [Y. Ando $et$ $al$., Phys. Rev. B61, (2000) 14956(R).], are not. We show that the quantitatively different hole-scales resulted in opposite conclusion of the same experimental observations. It can also lead to different interpretations of the electronic phase diagram when comparing different physical properties in different high-$T_c$ systems. We suggest that the $P_{pl}$-scale is the correct universal scale that works for all high-$T_c$ cuprates and it should be used for all quantitative doping dependence studies of cuprates.

cond-mat.supr-con↗

arXiv2013

Implications of Charge Ordering in the High Tc Cuprate Superconductors in the Far-infrared Spectroscopy

We addressed the issue of the absence of the far-infrared signatures pertaining to charge ordering in the published far-infrared reflectivity data of La2-xSrxCuO4 single crystals while other experimental probes unravel that charge ordering is a hallmark of the superconducting cuprates. Through direct comparison of the far-infrared data reported by various groups side by side and also with the Raman scattering data, we found that the inconsistencies stem from the failure in capturing delicate spectral features embedded in the close-to-perfect ab-plane far-infrared reflectivity of La2-xSrxCuO4 single crystals by misidentifying the reflectivity as the Drude-like metallic reflectivity. The analysis of the close-to-true reflectivity data reveals that only a small fraction (< 3 %) of the total doping-induced charge carriers (electrons) are itinerant on the electron lattice made up with the rest of the electrons (> 97 %) at all doping levels up to 16 %. We conclude that the far-infrared reflectivity study is far from being ready to construct a coherent picture of the ubiquitous charge ordering phenomenon and its relationship with the high Tc superconductivity.

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arXiv2012

In-plane and Out-of-plane Plasma Resonances in Optimally Doped La1.84Sr0.16CuO4

We addressed the inconsistency between the electron mass anisotropy ratios determined by the far-infrared experiments and DC conductivity measurements. By eliminating possible sources of error and increasing the sensitivity and resolution in the far-infrared reflectivity measurement on the single crystalline and on the polycrystalline La1.84Sr0.16CuO4, we have unambiguously identified that the source of the mass anisotropy problem is in the estimation of the free electron density involved in the charge transport and superconductivity. In this study we found that only 2.8 % of the total doping-induced charge density is itinerant at optimal doping. Our result not only resolves the mass anisotropy puzzle but also points to a novel electronic structure formed by the rest of the electrons that sets the stage for the high temperature superconductivity.

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arXiv2012

Unconventional magnetic phase diagram of cuprate superconductor La2-xSrxCuO4 at quantum critical point x = 1/9

We propose a new magnetic phase diagram of La2-xSrxCuO4 around a quantum critical point x = 1/9 based on field-cooled magnetization measurements and critical fittings. A new phase boundary Tm2(H) is discovered which buries deeply below the first order vortex melting line in the vortex solid phase. The coupling between superconductivity and antiferromagnetism is found to be attractive below Tm2(H) while repulsive above. The attractive coupling between superconducting order and static antiferromagnetic order provides compelling experimental evidence that the antiferromagnetism microscopically coexists and collaborates with the high temperature superconductivity in cuprates.

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arXiv2011

Observation of the predicted charge collective mode of the Tc = 45 K superconducting phase of La2CuO4+δ

We report the far-infrared (far-IR) observation of the Goldstone mode at ~ 72 cm-1 (~ 9 meV) predicted to exist in the superconducting phase of the transition temperature (Tc) at 45 K in the La2CuO4-based superconductors. Our observation furthers the experimental support for the two-component picture where the localized charge texture, formed at a specific planar hole density (Ppl), is tied to the HTS at Tc = 15 K, 30 K, and 45 K in a hierarchical fashion at the so-called "magic" doping level at Ppl = 1/16, 2/16, and 3/16 respectively.

cond-mat.supr-con↗

arXiv2010

Growth and hole density control through equilibrium oxygen annealing of optimally doped Y1-xCaxBa2Cu3O7-δ single crystals

We have grown calcium and oxygen co-doped Y1-xCaxBa2Cu3O7-δ single crystals using self-flux method. A method of fine tuning oxygen content to reach the equilibrium state through in situ monitoring of the conductivity change is established. Structural, compositional and electronic property characterizations of optimally co-doped Y1-xCaxBa2Cu3O7-δ crystals indicate that they are high quality equilibrium crystals with a sharp superconducting transition width of 0.2K.

cond-mat.supr-con↗

arXiv2010

Far-infrared measurements of oxygen-doped polycrystalline La2CuO4.0315 superconductor under slow-cooled and fast-cooled conditions

We have studied the far-infrared (far-IR) charge dynamics of an equilibrated pure oxygen doped La2CuO4+0.0315 under slow-cooled and fast-cooled conditions. The superconducting transition temperature (Tc) for the slow-cooled and that for the fast-cooled processes were respectively found to be close to the two intrinsic Tc's: One at 30 K and the other at 15 K. Direct comparison with our previous results and other far-IR and Raman studies on single crystalline La2-xSrxCuO4, we conclude that the topology of the pristine electronic phases that are responsible for the two intrinsic Tc's is holes arranged into two-dimensional (2D) square lattices.

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arXiv2008

Unified electronic phase diagram for hole-doped high-Tc cuprates

We have analyzed various characteristic temperatures and energies of hole-doped high-Tc cuprates as a function of a dimensionless hole-doping concentration (pu). Entirely based on the experimental grounds we construct a unified electronic phase diagram (UEPD), where three characteristic temperatures (T*'s) and their corresponding energies (E*'s) converge as pu increases in the underdoped regime. T*'s and E*'s merge together with the Tc curve and 3.5kBTc curve at pu - 1.1 in the overdoped regime, respectively. They finally go to zero at pu - 1.3. The UEPD follows an asymmetric half-dome-shaped Tc curve in which Tc appears at pu - 0.4, reaches a maximum at pu - 1, and rapidly goes to zero at pu - 1.3. The asymmetric half-dome-shaped Tc curve is at odds with the well-known symmetric superconducting dome for La2-xSrxCuO4 (SrD-La214), in which two characteristic temperatures and energies converge as pu increases and merge together at pu - 1.6, where Tc goes to zero. The UEPD clearly shows that pseudogap phase precedes and coexists with high temperature superconductivity in the underdoped and overdoped regimes, respectively. It is also clearly seen that the upper limit of high-Tc cuprate physics ends at a hole concentration that equals to 1.3 times the optimal doping concentration for almost all high-Tc cuprate materials, and 1.6 times the optimal doping concentration for the SrD-La214. Our analysis strongly suggests that pseudogap is a precursor of high-Tc superconductivity, the observed quantum critical point inside the superconducting dome may be related to the end point of UEPD, and the normal state of the underdoped and overdoped high temperature superconductors cannot be regarded as a conventional Fermi liquid phase.

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arXiv2006

Universal optimal hole-doping concentration in single-layer high-temperature cuprate superconductors

We argue that in cuprate physics there are two types, hole content per CuO$_2$ plane ($P_{pl}$) and the corresponding hole content per unit volume ($P_{3D}$), of hole-doping concentrations for addressing physical properties that are two-dimensional (2D) and three-dimensional (3D) in nature, respectively. We find that superconducting transition temperature ($T_c$) varies systematically with $P_{3D}$ as a superconducting \textquotedblleft $dome$\textquotedblright with a universal optimal hole-doping concentration $P_{3D}^{opt.}$ = 1.6 $\times$ 10$^{21}$ cm$^{-3}$ for single-layer high temperature superconductors. We suggest that $P_{3D}^{opt.}$ determines the upper bound of the electronic energy of underdoped single-layer high-$T_c$ cuprates.

cond-mat.supr-con↗

arXiv2006

Intrinsic electronic superconducting phases at 60 K and 90 K in double-layer YBa$_2$Cu$_3$O$_{6+δ}$

We study superconducting transition temperature ($T_c$) of oxygen-doped double-layer high-temperature superconductors YBa$_2$Cu$_3$O$_{6+δ}$ (0 $\le$ $δ$ $\le$ 1) as a function of the oxygen dopant concentration ($δ$) and planar hole-doping concentration ($P_{pl}$). We find that $T_c$, while clearly influenced by the development of the chain ordering as seen in the $T_c$ $vs.$ $δ$ plot, lies on a universal curve originating at the critical hole concentration ($P_c$) = 1/16 in the $T_c$ $vs.$ $P_{pl}$ plot. Our analysis suggests that the universal behavior of $T_c$($P_{pl}$) can be understood in terms of the competition and collaboration of chemical-phases and electronic-phases that exist in the system. We conclude that the global superconductivity behavior of YBa$_2$Cu$_3$O$_{6+δ}$ as a function of doping is electronically driven and dictated by pristine electronic phases at magic doping numbers that follow the hierarchical order based on $P_c$, such as 2 $\times$ $P_c$, 3 $\times$ $P_c$ and 4 $\times$ $P_c$. We find that there are at least two intrinsic electronic superconducting phases of $T_c$ = 60 K at 2 $\times$ $P_c$ = 1/8 and $T_c$ = 90 K at 3 $\times$ $P_c$ = 3/16.

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arXiv2006

Robust intrinsic electronic superconducting phases in underdoped La_{2-x}Sr_xCuO4 single crystals

We have measured the superconducting critical temperature (Tc) and the diamagnetic susceptibility of La2-xSrxCuO4 single crystals in various magnetic fields. We observed a field-induced evolution from an apparent Tc phase to an intrinsic Tc1 = 15 K or Tc2 = 30 K phase characterized by "magic" hole concentration which is commensurate with that of a two dimensional electronic lattice. The onset Tc of the intrinsic superconducting phases remains robust up to H = 5 Tesla. We suggest that the intrinsic superconducting phases at "magic" doping concentrations are the pristine electronic phases of high temperature superconductivity.

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arXiv2006

The "Bohr" Model for the High Tc Superconductivity

We propose a charge crystal model that captures all the essential physics of the high temperature superconductivity (HTS) in the long wavelength limit. Based on the recent transport and the far-infrared (far-IR) experiments, we argue that the three-dimensional (3D) ordering of the pinned two-dimensional (2D) square electronic lattice (EL) in each CuO2 plane is the building block of HTS. Incorporating the physical picture derived from the neutron scattering experiments, we demonstrate that our model presents a coherent picture of the HTS. We suggest that the charge crystal model serves as a model for the microscopic theory and, hence, offers the key to the mechanism for the HTS.

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arXiv2005

Evidence of Coherent C-Axis Charge Transport in Underdoped La2-xSrxCuO4 Superconductors

We have observed the plasma edge in the normal state c-axis far-infrared (far-IR) reflectivity of La2-xSrxCuO4 (LSCO) single crystals at an unlikely Sr-doping concentration x = 0.07 but not in x = 0.09. We find that the c-axis scattering rate (Gc) is surprisingly small, Gc = 13 (+_) 2 cm-1 for x = 0.07 and Gc = 24 (+_) 1 cm-1 for x = 0.09 and nearly temperature independent but increases linearly with doping up to x = 0.16. We suggest that the apparent absence of the normal state plasma edge in the previous measurements is due to the larger Gc than the screened plasma frequency of the coherent free carriers. We conclude that the c-axis charge transport in LSCO in the underdoped regime is intrinsically coherent.

cond-mat.supr-con↗

arXiv2004

A Universal Intrinsic Scale of Hole Concentration for High-Tc Cuprates

We have measured thermoelectric power (TEP) as a function of hole concentration per CuO2 layer, Ppl, in Y1-xCaxBa2Cu3O6 (Ppl = x/2) with no oxygen in the Cu-O chain layer. The room-temperature TEP as a function of Ppl, S290(Ppl), of Y1-xCaxBa2Cu3O6 behaves identically to that of La2-zSrzCuO4 (Ppl = z). We argue that S290(Ppl) represents a measure of the intrinsic equilibrium electronic states of doped holes and, therefore, can be used as a common scale for the carrier concentrations of layered cuprates. We shows that the Ppl determined by this new universal scale is consistent with both hole concentration microscopically determined by NQR and the hole concentration macroscopically determined by the Cu valency. We find two characteristic scaling temperatures, TS* and TS2*, in the TEP vs. temperature curves that change systematically with doping. Based on the universal scale, we uncover a universal phase diagram in which almost all the experimentally determined pseudogap temperatures as a function of Ppl fall on two common curves; upper pseudogap temperature defined by the TS* versus Ppl curve and lower pseudogap temperature defined by the TS2* versus Ppl curve. We find that while pseudogaps are intrinsic properties of doped holes of a single CuO2 layer for all high-Tc cuprates, Tc depends on the number of layers, therefore the inter-layer coupling, in each individual system.

cond-mat.supr-con↗

arXiv2003

The composite picture of the charge carriers in La2-xSrxCuO4 (0.063 < x < 0.11) superconductors

Through far-infrared studies of La2-xSrxCuO4 single crystals for x = 0.063, 0.07, 0.09, and 0.11, we found that only ~ 0.2 % of the total holes participated in the nearly dissipationless normal state charge transport and superconductivity. We have also observed characteristic collective modes at w ~ 18 cm-1 and 22 cm-1 due to the bound carriers in an electronic lattice (EL) state and the free carriers are massively screened by the EL. Our findings lead us to propose a composite picture of the charge system where the free carriers are coupled to and riding on the EL. This unique composite system of charge carriers may provide further insights into the understanding of the cuprate physics.

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arXiv2003

Anomalous superconducting properties at magic doping levels in under-doped La2-xSrxCuO4 single crystals

A series of high-quality under-doped La2-xSrxCuO4 superconductor crystals with x = 0.063 - 0.125 were prepared by traveling-solvent floating-zone (TSFZ) technique. We found by dc magnetic measurements that, in this series of crystals, the superconducting transition was quite sharp in the vicinity of the hole densities of x = 1/16 and x = 1/9 while it was much broader away from these two "magic numbers", and the Meissner fraction showed a remarkable minimum near x = 1/9. We concluded that these phenomena are reflections of intrinsic properties of this cuprate system. Our observations are discussed in light of recently proposed composite charge model together with charge inhomogeneity and electronic phase separations.

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