40 research outputs found
Why holes are not like electrons. II. The role of the electron-ion interaction
In recent work, we discussed the difference between electrons and holes in
energy band in solids from a many-particle point of view, originating in the
electron-electron interaction, and argued that it has fundamental consequences
for superconductivity. Here we discuss the fact that there is also a
fundamental difference between electrons and holes already at the single
particle level, arising from the electron-ion interaction. The difference
between electrons and holes due to this effect parallels the difference due to
electron-electron interactions: {\it holes are more dressed than electrons}. We
propose that superconductivity originates in 'undressing' of carriers from
electron-electron and electron-ion interactions, and that both aspects
of undressing have observable consequences.Comment: Continuation of Phys.Rev.B65, 184502 (2002) = cond-mat/0109385 (2001
Superconductivity from Undressing
Photoemission experiments in high cuprates indicate that quasiparticles
are heavily 'dressed' in the normal state, particularly in the low doping
regime. Furthermore these experiments show that a gradual undressing occurs
both in the normal state as the system is doped and the carrier concentration
increases, as well as at fixed carrier concentration as the temperature is
lowered and the system becomes superconducting. A similar picture can be
inferred from optical experiments. It is argued that these experiments can be
simply understood with the single assumption that the quasiparticle dressing is
a function of the local carrier concentration. Microscopic Hamiltonians
describing this physics are discussed. The undressing process manifests itself
in both the one-particle and two-particle Green's functions, hence leads to
observable consequences in photoemission and optical experiments respectively.
An essential consequence of this phenomenology is that the microscopic
Hamiltonians describing it break electron-hole symmetry: these Hamiltonians
predict that superconductivity will only occur for carriers with hole-like
character, as proposed in the theory of hole superconductivity
Preparation of the extracellular domain of the rabbit prolactin receptor expressed in Escherichia coli and its interaction with lactogenic hormones
International audienc
Improvement of PCR reaction conditions for site-directed mutagenesis of big plasmids
QuickChange mutagenesis is the method of choice for site-directed mutagenesis (SDM) of target sequences in a plasmid. It can be applied successfully to small plasmids (up to 10 kb). However, this method cannot efficiently mutate bigger plasmids. Using KOD Hot Start polymerase in combination with high performance liquid chromatography (HPLC) purified primers, we were able to achieve SDM in big plasmids (up to 16 kb) involving not only a single base change but also multiple base changes. Moreover, only six polymerase chain reaction (PCR) cycles and 0.5 µl of polymerase (instead of 18 PCR cycles and 1.0 µl of enzyme in the standard protocol) were sufficient for the reaction