band gap - 2024 ACF Winter

Question

This quantity is called “direct” if electrons have the same crystal momentum in the upper and lower levels that define it. For 10 points each:

[10m] Insulators have a high value of what quantity, which is the difference between namesake “valence” and “conduction” levels?

ANSWER: band gap [or energy gap; accept direct band gap; prompt on gap]

[10e] A medium-sized band gap characterizes these materials, as they exhibit properties between insulators and conductors.

ANSWER: semiconductors

[10h] Unlike a “transport” gap, a band gap with this name is the energy needed to produce an electron–hole pair that is bound together. This adjective also describes phonons in which two adjacent atoms vibrate in opposite directions, unlike acoustic phonons.

ANSWER: optical [accept optical band gap or optical phonons]

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Summary


2024 ACF Winter at UC Berkeley	2024-11-16	Y	3	23.33	100%	100%	33%
2024 ACF Winter at Clemson	2024-11-16	Y	8	16.25	100%	63%	0%
2024 ACF Winter at Ohio State	2024-11-16	Y	7	12.86	100%	29%	0%
2024 ACF Winter at Online	2024-11-16	Y	8	16.25	100%	63%	0%
2024 ACF Winter at UBC	2024-11-16	Y	3	16.67	100%	67%	0%
2024 ACF Winter at Central Florida	2024-11-16	Y	4	20.00	100%	100%	0%
2024 ACF Winter at Oxford	2024-11-16	Y	11	15.45	100%	36%	18%

Data


Berkeley B	Berkeley C	10	10	0	20
Stanford L	Berkeley A	10	10	0	20
Stanford M	Stanford A	10	10	10	30
Emory A	Alabama A	0	10	0	10
Auburn A	Georgia Tech C	10	10	0	20
Georgia Tech E	Auburn C	10	10	0	20
Georgia Tech A	Clemson A	10	10	0	20
Georgia Tech B	Auburn B	10	10	0	20
Emory B	Georgia Tech D	0	10	0	10
Georgia Tech F	Tennesse A	10	10	0	20
Tennesse B	South Carolina A	0	10	0	10
Ohio State A	CWRU B	10	10	0	20
Kenyon A (UG)	CWRU D (DII)	0	10	0	10
Michigan D (DII)	Michigan B	0	10	0	10
Michigan C (UG)	CWRU C (UG)	0	10	0	10
Ohio State C (DII)	Michigan State B (UG)	10	10	0	20
Ohio State B (DII)	Kenyon B (DII)	0	10	0	10
Pitt B (UG)	Michigan State C (UG)	0	10	0	10
NYU B	Arkansas	0	10	0	10
Oregon State	Iowa	10	10	0	20
McGill E	Mississippi State	0	10	0	10
Missouri	Colorado College	10	10	0	20
NYU A	Ole Miss	10	10	0	20
Texas A	Vassar B	10	10	0	20
Central Oklahoma	Texas C	0	10	0	10
WUSTL A	Texas D	10	10	0	20
Alberta	UW A	0	10	0	10
UBC A	SFU	10	10	0	20
UW B	UBC B	10	10	0	20
UCF A	UF E	10	10	0	20
UF D	UCF B	10	10	0	20
UF B	Florida State University A	10	10	0	20
UF A	UF C	10	10	0	20
Birmingham	Imperial B	10	10	0	20
Bristol B	LSE B	0	10	0	10
Cambridge B	Oxford A	10	10	10	30
Cambridge A	Cambridge C	10	10	0	20
Southampton	Cambridge D	0	10	0	10
Edinburgh	Durham B	0	10	0	10
LSE A	Bristol A	0	10	0	10
Imperial A	Manchester	10	10	0	20
Oxford B	Durham A	0	10	10	20
Southampton A	Warwick A	0	10	0	10
Vanderbilt	Warwick B	0	10	0	10