Biomedical subjects

D H Lu

Publications and source records attributed to D H Lu.

At least 19 recordsLinked to original sources

PubMed2006

Distinct Fermi-momentum-dependent energy gaps in deeply underdoped Bi2212.

We used angle-resolved photoemission spectroscopy applied to deeply underdoped cuprate superconductors Bi2Sr2Ca(1-x)YxCu2O8 (Bi2212) to reveal the presence of two distinct energy gaps exhibiting different doping dependence. One gap, associated with the antinodal region where no coherent peak is observed, increased with underdoping, a behavior known for more than a decade and considered as the general gap behavior in the underdoped regime. The other gap, associated with the near-nodal regime where a coherent peak in the spectrum can be observed, did not increase with less doping, a behavior not previously observed in the single particle spectra. We propose a two-gap scenario in momentum space that is consistent with other experiments and may contain important information on the mechanism of high-transition temperature superconductivity.

Journal Article↗

PubMed2006

Fermi surface and quasiparticle excitations of Sr2RhO4.

The electronic structure of the layered 4d transition metal oxide Sr2RhO4 is investigated by angle resolved photoemission. We find well-defined quasiparticle excitations with a highly anisotropic dispersion, suggesting a quasi-two-dimensional Fermi-liquid-like ground state. Markedly different from the isostructural Sr2RuO4, only two bands with dominant Rh 4dxz,zy character contribute to the Fermi surface. A quantitative analysis of the photoemission quasiparticle band structure is in excellent agreement with bulk data. In contrast, it is found that state-of-the-art density functional calculations in the local density approximation differ significantly from the experimental findings.

Journal Article↗

PubMed2006

Doping dependence of the coupling of electrons to bosonic modes in the single-layer high-temperature Bi2Sr2CuO6 superconductor.

A recent highlight in the study of high-T(c) superconductors is the observation of band renormalization or self-energy effects on the quasiparticles. This is seen in the form of kinks in the quasiparticle dispersions as measured by photoemission and interpreted as signatures of collective bosonic modes coupling to the electrons. Here we compare for the first time the self-energies in an optimally doped and strongly overdoped, nonsuperconducting single-layer Bi-cuprate (Bi2Sr2CuO6). In addition to the appearance of a strong overall weakening, we also find that the weight of the self-energy in the overdoped system shifts to higher energies. We present evidence that this is related to a change in the coupling to c-axis phonons due to the rapid change of the c-axis screening in this doping range.

Journal Article↗

PubMed2006

Nested fermi surface and electronic instability in Ca3Ru2O7.

High-resolution angular resolved photoemission data reveal well-defined quasiparticle bands of unusually low weight, emerging in line with the metallic phase of Ca(3)Ru(2)O(7) below approximately 30 K . At the bulk structural phase transition temperature of 48 K, we find clear evidence for an electronic instability, gapping large parts of the underlying Fermi surface that appears to be nested. Metallic pockets are found to survive in the small, non-nested sections, constituting a low-temperature Fermi surface with 2 orders of magnitude smaller volume than in all other metallic ruthenates. The Fermi velocities and volumes of these pockets are in agreement with the results of complementary quantum oscillation measurements on the same crystal batches.

Journal Article↗

PubMed2005

The aggressive form of cherubism: report of two cases in unrelated families.

Cherubism is a benign lesion that causes painless symmetrical enlargement of the jaws, usually with a familial tendency. We describe in two Chinese families two cases of the aggressive form of cherubism with extensive swelling on both sides of the mandible, typical microscopic findings, and apparent familial history.

Adult↗

PubMed2005

Nodal quasiparticles and antinodal charge ordering in Ca2-xNaxCuO2Cl2.

Understanding the role of competing states in the cuprates is essential for developing a theory for high-temperature superconductivity. We report angle-resolved photoemission spectroscopy experiments which probe the 4a0 x 4a0 charge-ordered state discovered by scanning tunneling microscopy in the lightly doped cuprate superconductor Ca2-xNaxCuO2Cl2. Our measurements reveal a marked dichotomy between the real- and momentum-space probes, for which charge ordering is emphasized in the tunneling measurements and photoemission is most sensitive to excitations near the node of the d-wave superconducting gap. These results emphasize the importance of momentum anisotropy in determining the complex electronic properties of the cuprates and places strong constraints on theoretical models of the charge-ordered state.

Journal Article↗

PubMed2004

Missing quasiparticles and the chemical potential puzzle in the doping evolution of the cuprate superconductors.

The evolution of Ca2-xNaxCuO2Cl2 from Mott insulator to superconductor was studied using angle-resolved photoemission spectroscopy. By measuring both the excitations near the Fermi energy as well as nonbonding states, we tracked the doping dependence of the electronic structure and the chemical potential with unprecedented precision. Our work reveals failures in the standard weakly interacting quasiparticle scenario, including the broad line shapes of the insulator and the apparently paradoxical shift of the chemical potential within the Mott gap. To resolve this, we develop a model where the quasiparticle is vanishingly small at half filling and grows upon doping, allowing us to unify properties such as the dispersion and Fermi wave vector with the chemical potential.

Journal Article↗

PubMed2004

Coupling of the B1g phonon to the antinodal electronic states of Bi2Sr2Ca0.92Y0.08Cu2O8+delta.

Angle-resolved photoemission spectroscopy on optimally doped Bi(2)Sr(2)Ca(0.92)Y(0.08)Cu(2)O(8+delta) uncovers a coupling of the electronic bands to a 40 meV mode in an extended k-space region away from the nodal direction, leading to a new interpretation of the strong renormalization of the electronic structure seen in Bi2212. Phenomenological agreements with neutron and Raman experiments suggest that this mode is the B(1g) oxygen bond-buckling phonon. A theoretical calculation based on this assignment reproduces the electronic renormalization seen in the data.

Journal Article↗

PubMed2002

Doping dependence of an n-type cuprate superconductor investigated by angle-resolved photoemission spectroscopy.

We present an angle-resolved photoemission doping dependence study of the n-type cuprate superconductor Nd(2-x)Ce(x)CuO(4+/-delta), from the half-filled Mott insulator to the T(c) = 24 K superconductor. In Nd2CuO4, we reveal the charge-transfer band for the first time. As electrons are doped into the system, this feature's intensity decreases with the concomitant formation of near- E(F) spectral weight. At low doping, the Fermi surface is an electron-pocket (with volume approximately x) centered at (pi,0). Further doping leads to the creation of a new holelike Fermi surface (volume approximately 1+x) centered at (pi,pi). These findings shed light on the Mott gap, its doping evolution, as well as the anomalous transport properties of the n-type cuprates.

Journal Article↗

PubMed2002

Electronic structure of MgB2 from angle-resolved photoemission spectroscopy.

The first angle-resolved photoemission spectroscopy results from MgB2 single crystals are reported. Along the GammaK and GammaM directions, we observed three distinct dispersive features approaching the Fermi energy. These can be assigned to the theoretically predicted sigma (B 2p(x,y)) and pi (B 2p(z)) bands. In addition, a small parabolic-like band is detected around the Gamma point, which can be attributed to a surface-derived state. The overall agreement between our results and the band calculations suggests that the electronic structure of MgB2 is of a conventional nature, thus implying that electron correlations are weak and may be of little importance to superconductivity in this system.

Journal Article↗

PubMed2002

Electronic structure of the trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta).

The low-energy electronic structure of the nearly optimally doped trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta) is investigated by angle-resolved photoemission spectroscopy. The normal state quasiparticle dispersion and Fermi surface and the superconducting d-wave gap and coherence peak are observed and compared with those of single- and bilayer systems. We find that both the superconducting gap magnitude and the relative coherence-peak intensity scale linearly with T(c) for various optimally doped materials.

Journal Article↗

PubMed2001

Anomalous electronic structure and pseudogap effects in Nd1.85Ce0.15CuO4.

We report a high-resolution angle-resolved photoemission spectroscopic study of the electron-doped ( n-type) cuprate superconductor Nd1.85Ce0.15CuO4. We observe regions along the Fermi surface where the near- E(F) intensity is suppressed and the spectral features are broad in a manner reminiscent of the high-energy "pseudogap" in the underdoped p-type (hole doped) cuprates. However, instead of occurring near the (pi,0) region, as in the p-type materials, this pseudogap falls near the intersection of the underlying Fermi surface with the antiferromagnetic Brillouin zone boundary.

Journal Article↗

PubMed2001

Bilayer splitting in the electronic structure of heavily overdoped Bi(2)Sr(2)CaCu(2)O(8+delta).

The electronic structure of heavily overdoped Bi(2)Sr(2)CaCu(2)O(8+delta) is investigated by angle-resolved photoemission spectroscopy. The long-sought bilayer band splitting in this two-plane system is observed in both normal and superconducting states, which qualitatively agrees with the bilayer Hubbard model calculations. The maximum bilayer energy splitting is about 88 meV for the normal state feature, while it is only about 20 meV for the superconducting peak.

Journal Article↗

PubMed2001

Superconducting gap and strong in-plane anisotropy in untwinned YBa2Cu3O(7-delta).

With significantly improved sample quality and instrumental resolution, we clearly identify in the ( pi,0) photoemission spectra from YBa(2)Cu(3)O(6.993), in the superconducting state, the long-sought "peak-dip-hump" structure. This advance allows us to investigate the large a-b anisotropy of the in-plane electronic structure including, in particular, a 50% difference in the magnitude of the superconducting gap that scales with the energy position of the hump feature. This anisotropy, likely induced by the presence of the CuO chains, raises serious questions about attempts to quantitatively explain the YBa(2)Cu(3)O(7-delta) data from various experiments using models based on a perfectly square lattice.

Journal Article↗

PubMed2001

Superconducting gap anisotropy in Nd1.85Ce0.15CuO4: results from photoemission.

We have performed angle resolved photoelectron spectroscopy on the electron doped cuprate superconductor Nd1.85Ce0.15CuO4. A comparison of the leading edge midpoints between the superconducting and normal states reveals a small, but finite shift of 1.5-2 meV near the ( pi,0) position, but no observable shift along the zone diagonal near ( pi/2, pi/2). This is interpreted as evidence for an anisotropic superconducting gap in the electron doped materials, which is consistent with the presence of d-wave superconducting order in this cuprate superconductor.

Journal Article↗

PubMed2001

[Expression of P21 WAF1/CIP1 in human astrocytomas in correlating with P53, MDM2, and cellular proliferation index].

OBJECTIVE: To study the correlation between the expression of p21, p53, MDM2 gene products and the initiation and progression of human astrocytomas. METHODS: The expression of P21, P53, MDM2, and proliferative cell nuclear antigen (PCNA) labeling index using immunohistochemistry in 41 paraffin embedded human astrocytoma samples. As well as the expression of p21 mRNA using mRNA in situ hybridization in 24 fresh human astrocytoma samples stored at -70 degrees C were investigated. In immunohistochemistry, we divided whole tumor cells by positive tumor cell nuclei to obtain labeling index (LI), in this way we could understand the protein product expression of gene in astrocytoma in different patients. In mRNA in situ hybridization, the expression of p21 mRNA was scored according to the rough percentage of positive cells. RESULTS: In p21 mRNA in situ hybridization, the positive staining was present in 87.5%. In immunohistochemistry, positive P21, P53, MDM2, and PCNA staining were presented in 75.6%, 68.3%, 65.9%, 100% respectively. Higher levels of P21 protein expression were seen in higher histological grade (P = 0.001). The association between P21 expression positively correlated with proliferation index. But not with P53 expression and MDM2 expression. The association between P53 expression and proliferation indices were statistically significant, but the expression of P53 was not related to tumor grade. There was no association between MDM2 expression and grade, or cellular proliferation index. Linear stepwise regression analysis showed the parameters affecting tumor grade were PCNA LI (P = 0.000) and P21 LI (P = 0.001). CONCLUSIONS: (1) Both p21 mRNA and P21 protein were overexpressed in human astrocytomas, the overexpression was related to cellular proliferation index, but was not related to P53 expression, suggesting there could be P53-independent pathway to induce the P21 expression, in addition, the overexpression of P21 alone appeared insufficient to suppress tumor growth, provided the participation of PCNA. (2) The expression of P53 protein was associated with proliferation indices, but was not with the tumor malignancy, this indicated that the inactivation of P53 might be the early event in the growth of human astrocytomas. (3) P21 labeling index and cellular proliferation index influenced the tumor histological grade, our data indicated that p21 gene might play a role in the progression of human astrocytomas.

Adolescent↗

PubMed1998

Food restriction differentially affects mRNAs encoding the major anterior pituitary tropic hormones.

Chronic food restriction (FR) leads to adaptive cellular changes, some of which retard aging. Moreover, some of these changes occur within weeks after onset of FR. Because neuroendocrine mechanisms may mediate these effects, we measured the effect of FR on the messenger ribonucleicacids (mRNAs) encoding all of the tropic hormones of the anterior pituitary (AP). Slot blot and solution hybridization were conducted on AP ribonucleicacid (RNA) samples obtained at 0500 h (AM) and 1500 h (PM) from 3-month-old male Fischer 344 rats fed ad libitum (AL) or FR (60% of AL calories) since 6 weeks of age. PolyA RNA/microgram total RNA was similar in AL and FR rats, indicating that there was no overall effect of FR on mRNA levels. The level of proopiomelanocortin (POMC) mRNA was not reduced by FR when expressed per microgram of RNA or as total AP content. By contrast, the total AP content of the mRNAs encoding LH beta, FSH beta, TSH beta, GH, and PRL was markedly reduced by FR. When expressed per microgram of RNA, however, only GH (AM and PM), FSH beta (AM), TSH beta (PM), and PRL (PM) were reduced by FR. These results reveal that FR differentially affects pituitary tropic hormone mRNA levels within weeks after onset of FR, and are consistent with a role for neuroendocrine alterations in the initiation of adaptive cellular responses to FR.

Animals↗

PubMed1994

[Immunohistochemical quantitative study of glial fibrillary acid protein and vimentin of astrocytomas].

Two different types of intermediate filaments, vimentin (VIM) and glial fibrillary acidic protein (GFAP) were studied by immunohistochemical quantitative analysis using image analyser in 25 cases of astrocytomas, grade II to IV. The results showed that the VIM and GFAP distribution patterns were similar in all cases of astrocytomas, but the expression of VIM in poorly differentiated astrocytoma (grade III and IV) being more frequent and intense than in well differentiated astrocytomas (grade II), the expression of GFAP in well differentiated astrocytomas (grade II) is more frequent and intense than in poorly differentiated astrocytomas (grade III and IV). We suggest that there is a negative relation between the reaction of GFAP and the degree of malignancy in astrocytomas and a positive correlation between reaction of VIM and the degree of malignancy in astrocytomas.

Astrocytoma↗