Photoinduced carriers in insulating cuprates: Fermi-glass state, metal-insulator transition and superconductivity
This dissertation studies the electronic properties of partially doped high-temperature superconducting (HTSC) cuprates by means of various optical and electric techniques, especially by subnanosecond transient photoconductivity ([sigma][sub ph]). Several important topics, which are at central focuses of the current HTSC field, are covered, including the localized electronic states in crystal cuprates, the nature of the metal-insulator (M-I) transition the phase separation, and the photoinduced metallic/superconducting droplets in HTSC cuprates. First, the necessary background materials are supplied, including a brief review of the structural and electronic properties in HTSC cuprates with emphasis on their variations via chemical doping. Then, the concept of photodoping in HTSC cuprates is developed. The transient photoinduced M-I transition in insulating cuprates is demonstrated through a series of [sigma][sub ph] experiments with subnanosecond temporal resolution. Under photoexcitation with [Dirac h][omega] > Eg, the resistivity in YBa[sub 2]Cu[sub 3]O[sub 6.3] is reduced by more than ten orders of magnitude at 100K or lower. The M-I transition is realized as indicated by the peak [sigma][sub ph] reaching the level of the minimum metallic conductivity, [sigma][sub min], and by the activation energy of [sigma][sub ph] approaching zero. The nature of this M-I transition is identified mainly due to the disorder induced localization, i.e., Anderson-type. On the dynamic aspect, at low excitation levels (I[sub L]), the decay of the [sigma][sub ph] in insulating crystals of YBa[sub 2]Cu[sub 3]O[sub 6.4] and La[sub 2]CuO[sub 4.013] is characterized by a power law decay, t[sup [minus]][alpha], with [alpha] [approx] 1, which is due to the dispersive transport commonly seen in disordered semiconductors, implying that the density of states at the Fermi level are localized (the Fermi-glass state).
- Research Organization:
- California Univ., Santa Barbara, CA (United States)
- OSTI ID:
- 7166481
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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CUPRATES
ELECTRICAL PROPERTIES
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BARIUM COMPOUNDS
DOPED MATERIALS
M1-TRANSITIONS
YTTRIUM COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
COPPER COMPOUNDS
ENERGY-LEVEL TRANSITIONS
MATERIALS
MULTIPOLE TRANSITIONS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS
360204* - Ceramics
Cermets
& Refractories- Physical Properties