Fermi-edge singularities in linear and nonlinear ultrafast spectroscopy

We discuss Fermi-edge singularity effects on the linear and nonlinear transient response of an electron gas in a doped semiconductor. We use a bosonization scheme to describe the low-energy excitations, which allows us to compute the time and temperature dependence of the response functions. Coherent control of the energy absorption at resonance is analyzed in the linear regime. It is shown that a phase shift appears in the coherent control oscillations, which is not present in the excitonic case. The nonlinear response is calculated analytically and used to predict that four wave-mixing experiments would present a Fermi-edge singularity when the exciting energy is varied. A new dephasing mechanism is predicted in doped samples that depends linearly on temperature and is produced by the low-energy bosonic excitations in the conduction band.

Are drawings dead? …and performance over aesthetics?

When the act of 'drawing' became what can only be called formalised, (whose growth can be said to have blossomed during the Renaissance), there developed a separation between the drawing and its procurement. Recently, David Ross Scheer, in his book ‘The Death of Drawing, Architecture in the Age of Simulation’ wrote: ‘…whereas architectural drawings exist to represent construction, architectural simulations exist to anticipate building performance.’ Meanwhile, Paolo Belardi, in his work ‘Why Architects Still Draw’ likens a drawing to an acorn, where he says: ‘It is the paradox of the acorn: a project emerges from a drawing – even from a sketch, rough and inchoate - just as an oak tree emerges from an acorn.’ He tells us that Giorgio Vasari would work late at night ‘seeking to solve the problems of perspective’ and he makes a passionate plea that this reflective process allows the concept to evolve, grow and/or develop. However, without belittling Belardi, the virtual model now needs this self-same treatment where it is nurtured, coaxed and encouraged to be the inchoate blueprint of the resultant oak tree. The model now too can embrace the creative process going through the first phase of preparation, where it focuses on the problem. The manipulation of the available material can then be incubated so that it is reasoned and generates feedback. This paper serves to align this shift in perception, methodologies and assess whether the 2D paper abstraction still has a purpose and role in today’s digital world!